diff --git a/packages/babel-helper-create-class-features-plugin/src/fields.ts b/packages/babel-helper-create-class-features-plugin/src/fields.ts
index 0f500852c8..9d8b386aa9 100644
--- a/packages/babel-helper-create-class-features-plugin/src/fields.ts
+++ b/packages/babel-helper-create-class-features-plugin/src/fields.ts
@@ -540,16 +540,31 @@ function buildPrivateInstanceFieldInitSpec(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateProperty>,
   privateNamesMap: PrivateNamesMap,
+  state,
 ) {
   const { id } = privateNamesMap.get(prop.node.key.id.name);
   const value = prop.node.value || prop.scope.buildUndefinedNode();
 
-  return template.statement.ast`${t.cloneNode(id)}.set(${ref}, {
-    // configurable is always false for private elements
-    // enumerable is always false for private elements
-    writable: true,
-    value: ${value},
-  })`;
+  if (!process.env.BABEL_8_BREAKING) {
+    if (!state.availableHelper("classPrivateFieldInitSpec")) {
+      return template.statement.ast`${t.cloneNode(id)}.set(${ref}, {
+        // configurable is always false for private elements
+        // enumerable is always false for private elements
+        writable: true,
+        value: ${value},
+      })`;
+    }
+  }
+
+  const helper = state.addHelper("classPrivateFieldInitSpec");
+  return template.statement.ast`${helper}(
+    ${t.thisExpression()},
+    ${t.cloneNode(id)},
+    {
+      writable: true,
+      value: ${value}
+    },
+  )`;
 }
 
 function buildPrivateStaticFieldInitSpec(
@@ -632,27 +647,87 @@ function buildPrivateInstanceMethodInitSpec(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateMethod>,
   privateNamesMap: PrivateNamesMap,
+  state,
 ) {
   const privateName = privateNamesMap.get(prop.node.key.id.name);
-  const { id, getId, setId, initAdded } = privateName;
+  const { getId, setId, initAdded } = privateName;
 
   if (initAdded) return;
 
   const isAccessor = getId || setId;
   if (isAccessor) {
-    privateNamesMap.set(prop.node.key.id.name, {
-      ...privateName,
-      initAdded: true,
-    });
+    return buildPrivateAccessorInitialization(
+      ref,
+      prop,
+      privateNamesMap,
+      state,
+    );
+  }
 
-    return template.statement.ast`
+  return buildPrivateInstanceMethodInitalization(
+    ref,
+    prop,
+    privateNamesMap,
+    state,
+  );
+}
+
+function buildPrivateAccessorInitialization(
+  ref: t.Expression,
+  prop: NodePath<t.ClassPrivateMethod>,
+  privateNamesMap: PrivateNamesMap,
+  state,
+) {
+  const privateName = privateNamesMap.get(prop.node.key.id.name);
+  const { id, getId, setId } = privateName;
+
+  privateNamesMap.set(prop.node.key.id.name, {
+    ...privateName,
+    initAdded: true,
+  });
+
+  if (!process.env.BABEL_8_BREAKING) {
+    if (!state.availableHelper("classPrivateFieldInitSpec")) {
+      return template.statement.ast`
       ${id}.set(${ref}, {
         get: ${getId ? getId.name : prop.scope.buildUndefinedNode()},
         set: ${setId ? setId.name : prop.scope.buildUndefinedNode()}
       });
     `;
+    }
   }
-  return template.statement.ast`${id}.add(${ref})`;
+
+  const helper = state.addHelper("classPrivateFieldInitSpec");
+  return template.statement.ast`${helper}(
+    ${t.thisExpression()},
+    ${t.cloneNode(id)},
+    {
+      get: ${getId ? getId.name : prop.scope.buildUndefinedNode()},
+      set: ${setId ? setId.name : prop.scope.buildUndefinedNode()}
+    },
+  )`;
+}
+
+function buildPrivateInstanceMethodInitalization(
+  ref: t.Expression,
+  prop: NodePath<t.ClassPrivateMethod>,
+  privateNamesMap: PrivateNamesMap,
+  state,
+) {
+  const privateName = privateNamesMap.get(prop.node.key.id.name);
+  const { id } = privateName;
+
+  if (!process.env.BABEL_8_BREAKING) {
+    if (!state.availableHelper("classPrivateMethodInitSpec")) {
+      return template.statement.ast`${id}.add(${ref})`;
+    }
+  }
+
+  const helper = state.addHelper("classPrivateMethodInitSpec");
+  return template.statement.ast`${helper}(
+    ${t.thisExpression()},
+    ${t.cloneNode(id)}
+  )`;
 }
 
 function buildPublicFieldInitLoose(
@@ -957,6 +1032,7 @@ export function buildFieldsInitNodes(
             // @ts-expect-error checked in switch
             prop,
             privateNamesMap,
+            state,
           ),
         );
         break;
@@ -985,6 +1061,7 @@ export function buildFieldsInitNodes(
             // @ts-expect-error checked in switch
             prop,
             privateNamesMap,
+            state,
           ),
         );
         pureStaticNodes.push(
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/input.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/input.js
new file mode 100644
index 0000000000..8bc7070673
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/input.js
@@ -0,0 +1,19 @@
+class Base {
+  constructor(obj) {
+    return obj;
+  }
+}
+
+class Derived extends Base {
+  get #foo() {
+    return 'bar';
+  }
+
+  set #foo(value) {
+    this.#foo = value;
+  }
+
+  static get(obj) {
+    return obj.#foo();
+  }
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/options.json b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/options.json
new file mode 100644
index 0000000000..608f30af0e
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/options.json
@@ -0,0 +1,6 @@
+{
+  "presets": [["env", { "shippedProposals": true }]],
+  "targets": {
+    "chrome": "75"
+  }
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/output.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/output.js
new file mode 100644
index 0000000000..f171007461
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-accessor/output.js
@@ -0,0 +1,31 @@
+class Base {
+  constructor(obj) {
+    return obj;
+  }
+
+}
+
+var _foo = /*#__PURE__*/new WeakMap();
+
+class Derived extends Base {
+  constructor(...args) {
+    super(...args);
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
+      get: _get_foo,
+      set: _set_foo
+    });
+  }
+
+  static get(obj) {
+    return babelHelpers.classPrivateFieldGet(obj, _foo).call(obj);
+  }
+
+}
+
+function _get_foo() {
+  return 'bar';
+}
+
+function _set_foo(value) {
+  babelHelpers.classPrivateFieldSet(this, _foo, value);
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/input.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/input.js
new file mode 100644
index 0000000000..902695e4e9
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/input.js
@@ -0,0 +1,13 @@
+class Base {
+  constructor(obj) {
+    return obj;
+  }
+}
+
+let counter = 0;
+class Derived extends Base {
+  #foo = ++counter;
+  static get(obj) {
+    return obj.#foo;
+  }
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/options.json b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/options.json
new file mode 100644
index 0000000000..608f30af0e
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/options.json
@@ -0,0 +1,6 @@
+{
+  "presets": [["env", { "shippedProposals": true }]],
+  "targets": {
+    "chrome": "75"
+  }
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/output.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/output.js
new file mode 100644
index 0000000000..59fe05cc06
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-field/output.js
@@ -0,0 +1,25 @@
+class Base {
+  constructor(obj) {
+    return obj;
+  }
+
+}
+
+let counter = 0;
+
+var _foo = /*#__PURE__*/new WeakMap();
+
+class Derived extends Base {
+  constructor(...args) {
+    super(...args);
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
+      writable: true,
+      value: ++counter
+    });
+  }
+
+  static get(obj) {
+    return babelHelpers.classPrivateFieldGet(obj, _foo);
+  }
+
+}
\ No newline at end of file
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/input.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/input.js
new file mode 100644
index 0000000000..1d65290406
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/input.js
@@ -0,0 +1,15 @@
+class Base {
+  constructor(obj) {
+    return obj;
+  }
+}
+
+class Derived extends Base {
+  #foo() {
+    return 'bar';
+  }
+
+  static get(obj) {
+    return obj.#foo();
+  }
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/options.json b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/options.json
new file mode 100644
index 0000000000..608f30af0e
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/options.json
@@ -0,0 +1,6 @@
+{
+  "presets": [["env", { "shippedProposals": true }]],
+  "targets": {
+    "chrome": "75"
+  }
+}
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/output.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/output.js
new file mode 100644
index 0000000000..f5dd07cc5e
--- /dev/null
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/field-reinitialization/private-method/output.js
@@ -0,0 +1,24 @@
+class Base {
+  constructor(obj) {
+    return obj;
+  }
+
+}
+
+var _foo = /*#__PURE__*/new WeakSet();
+
+class Derived extends Base {
+  constructor(...args) {
+    super(...args);
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
+  }
+
+  static get(obj) {
+    return babelHelpers.classPrivateMethodGet(obj, _foo, _foo2).call(obj);
+  }
+
+}
+
+function _foo2() {
+  return 'bar';
+}
\ No newline at end of file
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-private-methods/loose-false/output.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-private-methods/loose-false/output.js
index 6e921bc9e0..c74df0f555 100644
--- a/packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-private-methods/loose-false/output.js
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-private-methods/loose-false/output.js
@@ -2,7 +2,7 @@ var _privateMethod = /*#__PURE__*/new WeakSet();
 
 class X {
   constructor() {
-    _privateMethod.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _privateMethod);
   }
 
 }
diff --git a/packages/babel-helper-create-class-features-plugin/test/fixtures/replace-supers/method/output.js b/packages/babel-helper-create-class-features-plugin/test/fixtures/replace-supers/method/output.js
index af58f2d3c9..07429bb7b2 100644
--- a/packages/babel-helper-create-class-features-plugin/test/fixtures/replace-supers/method/output.js
+++ b/packages/babel-helper-create-class-features-plugin/test/fixtures/replace-supers/method/output.js
@@ -3,8 +3,7 @@ var _foo = /*#__PURE__*/new WeakSet();
 class A extends B {
   constructor(...args) {
     super(...args);
-
-    _foo.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
   }
 
 }
diff --git a/packages/babel-helpers/src/helpers.ts b/packages/babel-helpers/src/helpers.ts
index 7385e63a71..0911aee766 100644
--- a/packages/babel-helpers/src/helpers.ts
+++ b/packages/babel-helpers/src/helpers.ts
@@ -2022,6 +2022,32 @@ helpers.classPrivateMethodGet = helper("7.1.6")`
   }
 `;
 
+helpers.checkPrivateRedeclaration = helper("7.14.1")`
+  export default function _checkPrivateRedeclaration(obj, privateCollection) {
+    if (privateCollection.has(obj)) {
+      throw new TypeError("Cannot initialize the same private elements twice on an object");
+    }
+  }
+`;
+
+helpers.classPrivateFieldInitSpec = helper("7.14.1")`
+  import checkPrivateRedeclaration from "checkPrivateRedeclaration";
+
+  export default function _classPrivateFieldInitSpec(obj, privateMap, value) {
+    checkPrivateRedeclaration(obj, privateMap);
+    privateMap.set(obj, value);
+  }
+`;
+
+helpers.classPrivateMethodInitSpec = helper("7.14.1")`
+  import checkPrivateRedeclaration from "checkPrivateRedeclaration";
+
+  export default function _classPrivateMethodInitSpec(obj, privateSet) {
+    checkPrivateRedeclaration(obj, privateSet);
+    privateSet.add(obj);
+  }
+`;
+
 if (!process.env.BABEL_8_BREAKING) {
   // Use readOnlyError instead
   helpers.classPrivateMethodSet = helper("7.1.6")`
diff --git a/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration-optional-chaining/output.mjs b/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration-optional-chaining/output.mjs
index b9c029038b..982de80500 100644
--- a/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration-optional-chaining/output.mjs
+++ b/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration-optional-chaining/output.mjs
@@ -4,11 +4,10 @@ class C {
   constructor() {
     var _babelHelpers$classPr;
 
-    _m.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _m, {
       writable: true,
       value: void 0
     });
-
     const o = null;
     const n = this;
     const p = o === null || o === void 0 ? void 0 : babelHelpers.classPrivateFieldGet(o, _m).call(o, ...c, 1);
diff --git a/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration/output.mjs b/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration/output.mjs
index b9c029038b..982de80500 100644
--- a/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration/output.mjs
+++ b/packages/babel-plugin-bugfix-v8-spread-parameters-in-optional-chaining/test/fixtures/basic/class-private-integration/output.mjs
@@ -4,11 +4,10 @@ class C {
   constructor() {
     var _babelHelpers$classPr;
 
-    _m.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _m, {
       writable: true,
       value: void 0
     });
-
     const o = null;
     const n = this;
     const p = o === null || o === void 0 ? void 0 : babelHelpers.classPrivateFieldGet(o, _m).call(o, ...c, 1);
diff --git a/packages/babel-plugin-proposal-async-generator-functions/test/fixtures/async-generators/class-private-method/output.js b/packages/babel-plugin-proposal-async-generator-functions/test/fixtures/async-generators/class-private-method/output.js
index edaf639ec2..92c4e90b13 100644
--- a/packages/babel-plugin-proposal-async-generator-functions/test/fixtures/async-generators/class-private-method/output.js
+++ b/packages/babel-plugin-proposal-async-generator-functions/test/fixtures/async-generators/class-private-method/output.js
@@ -2,7 +2,7 @@ var _g = /*#__PURE__*/new WeakSet();
 
 class C {
   constructor() {
-    _g.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _g);
   }
 
 }
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/1-helpermemberexpressionfunction/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/1-helpermemberexpressionfunction/output.js
index 89ad20142e..ff85bfa459 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/1-helpermemberexpressionfunction/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/1-helpermemberexpressionfunction/output.js
@@ -5,8 +5,7 @@ var D = /*#__PURE__*/function () {
 
   function D() {
     babelHelpers.classCallCheck(this, D);
-
-    _arr.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _arr, {
       writable: true,
       value: void 0
     });
@@ -30,8 +29,7 @@ var C = /*#__PURE__*/function () {
 
   function C() {
     babelHelpers.classCallCheck(this, C);
-
-    _p.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _p, {
       writable: true,
       value: void 0
     });
@@ -55,8 +53,7 @@ var E = /*#__PURE__*/function () {
 
   function E() {
     babelHelpers.classCallCheck(this, E);
-
-    _arr2.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _arr2, {
       writable: true,
       value: void 0
     });
@@ -80,8 +77,7 @@ var F = /*#__PURE__*/function () {
 
   function F() {
     babelHelpers.classCallCheck(this, F);
-
-    _ar.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _ar, {
       writable: true,
       value: void 0
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/assignment/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/assignment/output.js
index a7817db0ff..e0c46183b8 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/assignment/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/assignment/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 0
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/call/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/call/output.js
index 27947d1df6..2b12c7ae9b 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/call/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/call/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: function () {
         return this;
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/canonical/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/canonical/output.js
index e41035c447..5fc50758bc 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/canonical/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/canonical/output.js
@@ -7,17 +7,14 @@ var Point = /*#__PURE__*/function () {
 
   function Point(x = 0, y = 0) {
     babelHelpers.classCallCheck(this, Point);
-
-    _x.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _x, {
       writable: true,
       value: void 0
     });
-
-    _y.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _y, {
       writable: true,
       value: void 0
     });
-
     babelHelpers.classPrivateFieldSet(this, _x, +x);
     babelHelpers.classPrivateFieldSet(this, _y, +y);
   }
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/constructor-collision/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/constructor-collision/output.js
index 05d01f4911..134fb98bde 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/constructor-collision/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/constructor-collision/output.js
@@ -6,11 +6,9 @@ var Foo = function Foo() {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _bar.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _bar, {
     writable: true,
     value: foo
   });
-
   var _foo = "foo";
 };
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/declaration-order/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/declaration-order/output.js
index b2c777ecc3..f3620fbdc8 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/declaration-order/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/declaration-order/output.js
@@ -5,8 +5,7 @@ var C = function C() {
 
   babelHelpers.classCallCheck(this, C);
   babelHelpers.defineProperty(this, "y", babelHelpers.classPrivateFieldGet(this, _x));
-
-  _x.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _x, {
     writable: true,
     value: void 0
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived-multiple-supers/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived-multiple-supers/output.js
index 06197e31d4..692b0bf2c2 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived-multiple-supers/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived-multiple-supers/output.js
@@ -14,15 +14,13 @@ var Foo = /*#__PURE__*/function (_Bar) {
 
     if (condition) {
       _this = _super.call(this);
-
-      _bar.set(babelHelpers.assertThisInitialized(_this), {
+      babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _bar, {
         writable: true,
         value: "foo"
       });
     } else {
       _this = _super.call(this);
-
-      _bar.set(babelHelpers.assertThisInitialized(_this), {
+      babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _bar, {
         writable: true,
         value: "foo"
       });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived/output.js
index 97251962ae..d215894182 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/derived/output.js
@@ -4,8 +4,7 @@ var Foo = function Foo() {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _prop.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _prop, {
     writable: true,
     value: "foo"
   });
@@ -25,12 +24,10 @@ var Bar = /*#__PURE__*/function (_Foo) {
 
     babelHelpers.classCallCheck(this, Bar);
     _this = _super.call(this, ...args);
-
-    _prop2.set(babelHelpers.assertThisInitialized(_this), {
+    babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _prop2, {
       writable: true,
       value: "bar"
     });
-
     return _this;
   }
 
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-1/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-1/output.js
index 1b13a2e595..f8813d3f02 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-1/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-1/output.js
@@ -4,12 +4,10 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   babelHelpers.classPrivateFieldSet(this, _client, 1);
   [this.x = babelHelpers.classPrivateFieldGet(this, _client), babelHelpers.classPrivateFieldDestructureSet(this, _client).value, this.y = babelHelpers.classPrivateFieldGet(this, _client)] = props;
 };
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-2/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-2/output.js
index 2ace67a331..9f88740d83 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-2/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-2/output.js
@@ -4,11 +4,9 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   [x, ...babelHelpers.classPrivateFieldDestructureSet(this, _client).value] = props;
 };
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-3/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-3/output.js
index 6b9882ec1b..091bdecc0d 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-3/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern-3/output.js
@@ -4,11 +4,9 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   [babelHelpers.classPrivateFieldDestructureSet(this, _client).value = 5] = props;
 };
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern/output.js
index ffeb7c001e..eeae89405a 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-array-pattern/output.js
@@ -4,11 +4,9 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   [babelHelpers.classPrivateFieldDestructureSet(this, _client).value] = props;
 };
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-1/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-1/output.js
index bb48cc08e1..2522895f07 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-1/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-1/output.js
@@ -4,12 +4,10 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   babelHelpers.classPrivateFieldSet(this, _client, 'foo');
   ({
     x: this.x = babelHelpers.classPrivateFieldGet(this, _client),
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-2/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-2/output.js
index 1ffd2fe58f..94f7111188 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-2/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-2/output.js
@@ -4,12 +4,10 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   ({
     x,
     ...babelHelpers.classPrivateFieldDestructureSet(this, _client).value
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-3/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-3/output.js
index 0c41925895..071bae2f50 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-3/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern-3/output.js
@@ -4,12 +4,10 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   ({
     x: babelHelpers.classPrivateFieldDestructureSet(this, _client).value = 5
   } = props);
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern/output.js
index 7459b76bc9..6366d6e7f5 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/destructuring-object-pattern/output.js
@@ -4,12 +4,10 @@ var Foo = function Foo(props) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _client.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _client, {
     writable: true,
     value: void 0
   });
-
   ({
     client: babelHelpers.classPrivateFieldDestructureSet(this, _client).value
   } = props);
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/extracted-this/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/extracted-this/output.js
index 1fb7de2ab4..5bbb120d1a 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/extracted-this/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/extracted-this/output.js
@@ -8,13 +8,11 @@ var Foo = function Foo(_foo) {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _bar.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _bar, {
     writable: true,
     value: this
   });
-
-  _baz.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _baz, {
     writable: true,
     value: foo
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/foobar/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/foobar/output.js
index 2ae9b573b3..496503850a 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/foobar/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/foobar/output.js
@@ -12,14 +12,12 @@ var Child = /*#__PURE__*/function (_Parent) {
 
     babelHelpers.classCallCheck(this, Child);
     _this = _super.call(this);
-
-    _scopedFunctionWithThis.set(babelHelpers.assertThisInitialized(_this), {
+    babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _scopedFunctionWithThis, {
       writable: true,
       value: () => {
         _this.name = {};
       }
     });
-
     return _this;
   }
 
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance-undefined/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance-undefined/output.js
index 8c8ba57dec..dfa75cf39d 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance-undefined/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance-undefined/output.js
@@ -4,8 +4,7 @@ var Foo = function Foo() {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _bar.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _bar, {
     writable: true,
     value: void 0
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance/output.js
index c7208f4d74..c30d93994e 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/instance/output.js
@@ -4,8 +4,7 @@ var Foo = function Foo() {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _bar.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _bar, {
     writable: true,
     value: "foo"
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/logical-assignment/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/logical-assignment/output.js
index e61da807ce..012356bcec 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/logical-assignment/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/logical-assignment/output.js
@@ -6,17 +6,15 @@ var _or = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _nullish.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _nullish, {
       writable: true,
       value: 0
     });
-
-    _and.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _and, {
       writable: true,
       value: 0
     });
-
-    _or.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _or, {
       writable: true,
       value: 0
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/multiple/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/multiple/output.js
index fd609d4458..de23ee50d1 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/multiple/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/multiple/output.js
@@ -6,13 +6,11 @@ var Foo = function Foo() {
   "use strict";
 
   babelHelpers.classCallCheck(this, Foo);
-
-  _x.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _x, {
     writable: true,
     value: 0
   });
-
-  _y.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _y, {
     writable: true,
     value: babelHelpers.classPrivateFieldGet(this, _x)
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/native-classes/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/native-classes/output.js
index 98f4973499..cca3df0b1e 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/native-classes/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/native-classes/output.js
@@ -2,7 +2,7 @@ var _bar = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _bar.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _bar, {
       writable: true,
       value: "bar"
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed-redeclared/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed-redeclared/output.js
index 1dd4c23b4a..1f1a88576b 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed-redeclared/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed-redeclared/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
@@ -24,8 +23,7 @@ var Foo = /*#__PURE__*/function () {
       var Nested = /*#__PURE__*/function (_babelHelpers$classPr2) {
         function Nested() {
           babelHelpers.classCallCheck(this, Nested);
-
-          _foo2.set(this, {
+          babelHelpers.classPrivateFieldInitSpec(this, _foo2, {
             writable: true,
             value: 2
           });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed/output.js
index e5d21a9466..73762088ae 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-computed/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed-redeclared/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed-redeclared/output.js
index 816f80cbeb..05370b34fc 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed-redeclared/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed-redeclared/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
@@ -31,12 +30,10 @@ var Foo = /*#__PURE__*/function () {
 
           babelHelpers.classCallCheck(this, Nested);
           _this = _super.call(this, ...args);
-
-          _foo2.set(babelHelpers.assertThisInitialized(_this), {
+          babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _foo2, {
             writable: true,
             value: 3
           });
-
           return _this;
         }
 
@@ -44,12 +41,10 @@ var Foo = /*#__PURE__*/function () {
       }((_foo3 = /*#__PURE__*/new WeakMap(), _babelHelpers$classPr = babelHelpers.classPrivateFieldGet(this, _foo3), /*#__PURE__*/function () {
         function _class2() {
           babelHelpers.classCallCheck(this, _class2);
-
-          _foo3.set(this, {
+          babelHelpers.classPrivateFieldInitSpec(this, _foo3, {
             writable: true,
             value: 2
           });
-
           babelHelpers.defineProperty(this, _babelHelpers$classPr, 2);
         }
 
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed/output.js
index dddde36ed4..378e354e71 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-extends-computed/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
@@ -29,12 +28,10 @@ var Foo = /*#__PURE__*/function () {
 
           babelHelpers.classCallCheck(this, Nested);
           _this = _super.call(this, ...args);
-
-          _foo2.set(babelHelpers.assertThisInitialized(_this), {
+          babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _foo2, {
             writable: true,
             value: 3
           });
-
           return _this;
         }
 
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-other-redeclared/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-other-redeclared/output.js
index 080795751a..134b4cab21 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-other-redeclared/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-other-redeclared/output.js
@@ -7,13 +7,11 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
-
-    _bar.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _bar, {
       writable: true,
       value: 1
     });
@@ -27,8 +25,7 @@ var Foo = /*#__PURE__*/function () {
       var Nested = /*#__PURE__*/function () {
         function Nested() {
           babelHelpers.classCallCheck(this, Nested);
-
-          _bar2.set(this, {
+          babelHelpers.classPrivateFieldInitSpec(this, _bar2, {
             writable: true,
             value: 2
           });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-redeclared/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-redeclared/output.js
index 1030037c7a..a507af4249 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-redeclared/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class-redeclared/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
@@ -20,8 +19,7 @@ var Foo = /*#__PURE__*/function () {
       var Nested = /*#__PURE__*/function () {
         function Nested() {
           babelHelpers.classCallCheck(this, Nested);
-
-          _foo2.set(this, {
+          babelHelpers.classPrivateFieldInitSpec(this, _foo2, {
             writable: true,
             value: 2
           });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class/output.js
index 69123eded4..df432fc79a 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/nested-class/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/optional-chain-member-optional-call-spread-arguments/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/optional-chain-member-optional-call-spread-arguments/output.js
index 593a5772ca..58e1533d26 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/optional-chain-member-optional-call-spread-arguments/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/optional-chain-member-optional-call-spread-arguments/output.js
@@ -2,7 +2,7 @@ var _m = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _m.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _m, {
       writable: true,
       value: void 0
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/private-in-derived/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/private-in-derived/output.js
index 1e57996600..f2c1dbcfb0 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/private-in-derived/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/private-in-derived/output.js
@@ -4,8 +4,7 @@ var Outer = function Outer() {
   "use strict";
 
   babelHelpers.classCallCheck(this, Outer);
-
-  _outer.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _outer, {
     writable: true,
     value: void 0
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reevaluated/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reevaluated/output.js
index 8c6a955412..6c22c5c9bf 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reevaluated/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reevaluated/output.js
@@ -3,7 +3,7 @@ function classFactory() {
 
   return _temp = (_foo = /*#__PURE__*/new WeakMap(), _class = class Foo {
     constructor() {
-      _foo.set(this, {
+      babelHelpers.classPrivateFieldInitSpec(this, _foo, {
         writable: true,
         value: "foo"
       });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reference-in-other-property/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reference-in-other-property/output.js
index 0b7476ce49..6c3d52803c 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reference-in-other-property/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/reference-in-other-property/output.js
@@ -9,20 +9,16 @@ var Foo = function Foo() {
 
   babelHelpers.classCallCheck(this, Foo);
   babelHelpers.defineProperty(this, "one", babelHelpers.classPrivateFieldGet(this, _private));
-
-  _two.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _two, {
     writable: true,
     value: babelHelpers.classPrivateFieldGet(this, _private)
   });
-
-  _private.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _private, {
     writable: true,
     value: 0
   });
-
   babelHelpers.defineProperty(this, "three", babelHelpers.classPrivateFieldGet(this, _private));
-
-  _four.set(this, {
+  babelHelpers.classPrivateFieldInitSpec(this, _four, {
     writable: true,
     value: babelHelpers.classPrivateFieldGet(this, _private)
   });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/regression-T7364/output.mjs b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/regression-T7364/output.mjs
index ae07dabb78..7d23ce353b 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/regression-T7364/output.mjs
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/regression-T7364/output.mjs
@@ -4,7 +4,7 @@ class MyClass {
   constructor() {
     var _this = this;
 
-    _myAsyncMethod.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _myAsyncMethod, {
       writable: true,
       value: function () {
         var _ref = babelHelpers.asyncToGenerator(function* () {
@@ -26,7 +26,7 @@ var _myAsyncMethod2 = /*#__PURE__*/new WeakMap();
   constructor() {
     var _this2 = this;
 
-    _myAsyncMethod2.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _myAsyncMethod2, {
       writable: true,
       value: function () {
         var _ref2 = babelHelpers.asyncToGenerator(function* () {
@@ -48,7 +48,7 @@ export default class MyClass3 {
   constructor() {
     var _this3 = this;
 
-    _myAsyncMethod3.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _myAsyncMethod3, {
       writable: true,
       value: function () {
         var _ref3 = babelHelpers.asyncToGenerator(function* () {
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-call/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-call/output.js
index 78bcdf3764..c329d248e3 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-call/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-call/output.js
@@ -28,12 +28,10 @@ var B = /*#__PURE__*/function (_A) {
 
     babelHelpers.classCallCheck(this, B);
     _this = _super.call(this, ...args);
-
-    _foo.set(babelHelpers.assertThisInitialized(_this), {
+    babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _foo, {
       writable: true,
       value: babelHelpers.get((_thisSuper = babelHelpers.assertThisInitialized(_this), babelHelpers.getPrototypeOf(B.prototype)), "foo", _thisSuper).call(_thisSuper)
     });
-
     return _this;
   }
 
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-expression/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-expression/output.js
index 1f17e973a2..d3b2bb1e9e 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-expression/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-expression/output.js
@@ -11,7 +11,7 @@ var Foo = /*#__PURE__*/function (_Bar) {
     var _temp, _this;
 
     babelHelpers.classCallCheck(this, Foo);
-    foo((_temp = _this = _super.call(this), _bar.set(babelHelpers.assertThisInitialized(_this), {
+    foo((_temp = _this = _super.call(this), babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _bar, {
       writable: true,
       value: "foo"
     }), _temp));
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-statement/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-statement/output.js
index e652b376af..310bfc691c 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-statement/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/super-statement/output.js
@@ -12,12 +12,10 @@ var Foo = /*#__PURE__*/function (_Bar) {
 
     babelHelpers.classCallCheck(this, Foo);
     _this = _super.call(this);
-
-    _bar.set(babelHelpers.assertThisInitialized(_this), {
+    babelHelpers.classPrivateFieldInitSpec(babelHelpers.assertThisInitialized(_this), _bar, {
       writable: true,
       value: "foo"
     });
-
     return _this;
   }
 
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/tagged-template/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/tagged-template/output.js
index b06497c1fc..530024699b 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/tagged-template/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/tagged-template/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _tag.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _tag, {
       writable: true,
       value: void 0
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/update/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/update/output.js
index 59d092de2d..cab004ed47 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/private/update/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/private/update/output.js
@@ -5,8 +5,7 @@ var Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 0
     });
diff --git a/packages/babel-plugin-proposal-class-properties/test/fixtures/regression/8882/output.js b/packages/babel-plugin-proposal-class-properties/test/fixtures/regression/8882/output.js
index f41cc8189c..fc17c143e2 100644
--- a/packages/babel-plugin-proposal-class-properties/test/fixtures/regression/8882/output.js
+++ b/packages/babel-plugin-proposal-class-properties/test/fixtures/regression/8882/output.js
@@ -8,8 +8,7 @@ for (let i = 0; i <= 10; ++i) {
   classes.push((_temp = (_bar = /*#__PURE__*/new WeakMap(), _i = i, _class = class A {
     constructor() {
       babelHelpers.defineProperty(this, _i, `computed field ${i}`);
-
-      _bar.set(this, {
+      babelHelpers.classPrivateFieldInitSpec(this, _bar, {
         writable: true,
         value: `private field ${i}`
       });
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/basic/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/basic/output.js
index 658554a063..4b64a3333d 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/basic/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/basic/output.js
@@ -4,16 +4,14 @@ var _privateFieldValue = /*#__PURE__*/new WeakMap();
 
 class Cl {
   constructor() {
-    _privateFieldValue.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateFieldValue, {
       get: _get_privateFieldValue,
       set: _set_privateFieldValue
     });
-
-    _privateField.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateField, {
       writable: true,
       value: "top secret string"
     });
-
     this.publicField = "not secret string";
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/get-only-setter/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/get-only-setter/output.js
index 2a0691beef..6c95f5f1bb 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/get-only-setter/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/get-only-setter/output.js
@@ -4,16 +4,14 @@ var _privateFieldValue = /*#__PURE__*/new WeakMap();
 
 class Cl {
   constructor() {
-    _privateFieldValue.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateFieldValue, {
       get: void 0,
       set: _set_privateFieldValue
     });
-
-    _privateField.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateField, {
       writable: true,
       value: 0
     });
-
     this.publicField = (this, babelHelpers.writeOnlyError("#privateFieldValue"));
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/reassignment/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/reassignment/output.js
index 4ee6f05ac8..3cd48da10e 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/reassignment/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/reassignment/output.js
@@ -4,11 +4,10 @@ var _privateFieldValue = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _privateFieldValue.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateFieldValue, {
       get: _get_privateFieldValue,
       set: void 0
     });
-
     this.self, results.push(2), babelHelpers.readOnlyError("#privateFieldValue");
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/set-only-getter/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/set-only-getter/output.js
index 52a97f6ec2..99848e09ac 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/set-only-getter/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/set-only-getter/output.js
@@ -9,16 +9,14 @@ class Cl {
   }
 
   constructor() {
-    _privateFieldValue.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateFieldValue, {
       get: _get_privateFieldValue,
       set: void 0
     });
-
-    _privateField.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateField, {
       writable: true,
       value: 0
     });
-
     babelHelpers.defineProperty(this, "counter", 0);
     this.self, 1([babelHelpers.classPrivateFieldDestructureSet(this.self, _privateFieldValue).value] = [1]), babelHelpers.readOnlyError("#privateFieldValue");
   }
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/tagged-template/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/tagged-template/output.js
index 90a909b22b..c8b534f929 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/tagged-template/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/tagged-template/output.js
@@ -2,11 +2,10 @@ var _tag = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _tag.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _tag, {
       get: _get_tag,
       set: void 0
     });
-
     babelHelpers.classPrivateFieldGet(this, _tag).bind(this)``;
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/updates/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/updates/output.js
index 0da9a9fc07..a3e609e11f 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/updates/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/accessors/updates/output.js
@@ -4,16 +4,14 @@ var _privateFieldValue = /*#__PURE__*/new WeakMap();
 
 class Cl {
   constructor() {
-    _privateFieldValue.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateFieldValue, {
       get: _get_privateFieldValue,
       set: _set_privateFieldValue
     });
-
-    _privateField.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateField, {
       writable: true,
       value: "top secret string"
     });
-
     this.publicField = "not secret string";
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/assumption-constantSuper/private-method-super/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/assumption-constantSuper/private-method-super/output.js
index 74762cfc04..b0c6dcfb4a 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/assumption-constantSuper/private-method-super/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/assumption-constantSuper/private-method-super/output.js
@@ -10,8 +10,7 @@ var _privateMethod = /*#__PURE__*/new WeakSet();
 class Sub extends Base {
   constructor(...args) {
     super(...args);
-
-    _privateMethod.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _privateMethod);
   }
 
   superMethod() {
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/get-set/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/get-set/output.js
index 995151f762..e4e64c0f34 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/get-set/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/get-set/output.js
@@ -4,12 +4,11 @@ var _getSet = /*#__PURE__*/new WeakMap();
 
 class Cl {
   constructor() {
-    _getSet.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _getSet, {
       get: _get_getSet,
       set: _set_getSet
     });
-
-    _privateField.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateField, {
       writable: true,
       value: 0
     });
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/set-get/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/set-get/output.js
index 3c26592e76..10379c8a37 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/set-get/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/duplicated-names/set-get/output.js
@@ -4,12 +4,11 @@ var _getSet = /*#__PURE__*/new WeakMap();
 
 class Cl {
   constructor() {
-    _getSet.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _getSet, {
       get: _get_getSet,
       set: _set_getSet
     });
-
-    _privateField.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _privateField, {
       writable: true,
       value: 0
     });
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/assignment/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/assignment/output.js
index 0c4c7958ab..368062ce9a 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/assignment/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/assignment/output.js
@@ -2,8 +2,7 @@ var _privateMethod = /*#__PURE__*/new WeakSet();
 
 class Foo {
   constructor() {
-    _privateMethod.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _privateMethod);
     this.publicField = babelHelpers.classPrivateMethodGet(this, _privateMethod, _privateMethod2).call(this);
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/async/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/async/output.js
index 256f7fe629..13ee286f7c 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/async/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/async/output.js
@@ -2,7 +2,7 @@ var _foo = /*#__PURE__*/new WeakSet();
 
 class Cl {
   constructor() {
-    _foo.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
   }
 
   test() {
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/before-fields/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/before-fields/output.js
index 447aba2a50..fe5a043218 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/before-fields/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/before-fields/output.js
@@ -4,11 +4,9 @@ var _method = /*#__PURE__*/new WeakSet();
 
 class Cl {
   constructor() {
-    _method.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _method);
     babelHelpers.defineProperty(this, "prop", babelHelpers.classPrivateMethodGet(this, _method, _method2).call(this, 1));
-
-    _priv.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _priv, {
       writable: true,
       value: babelHelpers.classPrivateMethodGet(this, _method, _method2).call(this, 2)
     });
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/class-expression/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/class-expression/output.js
index f0c034edfe..b177284a78 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/class-expression/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/class-expression/output.js
@@ -2,7 +2,7 @@ var _foo;
 
 console.log((_foo = /*#__PURE__*/new WeakSet(), class A {
   constructor() {
-    _foo.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
   }
 
   method() {
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/context/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/context/output.js
index 0be6a465b0..9d96c81401 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/context/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/context/output.js
@@ -2,8 +2,7 @@ var _getStatus = /*#__PURE__*/new WeakSet();
 
 class Foo {
   constructor(status) {
-    _getStatus.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _getStatus);
     this.status = status;
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/exfiltrated/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/exfiltrated/output.js
index 88d1606b8f..cac29e2bd1 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/exfiltrated/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/exfiltrated/output.js
@@ -4,7 +4,7 @@ var _privateMethod = /*#__PURE__*/new WeakSet();
 
 class Foo {
   constructor() {
-    _privateMethod.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _privateMethod);
 
     if (exfiltrated === undefined) {
       exfiltrated = babelHelpers.classPrivateMethodGet(this, _privateMethod, _privateMethod2);
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/generator/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/generator/output.js
index 2d3984fd5d..565cde34ac 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/generator/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/generator/output.js
@@ -2,7 +2,7 @@ var _foo = /*#__PURE__*/new WeakSet();
 
 class Cl {
   constructor() {
-    _foo.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
   }
 
   test() {
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/read-only/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/read-only/output.js
index 9b9b5db279..cf55c30531 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/read-only/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/read-only/output.js
@@ -7,8 +7,7 @@ class A {
   }
 
   constructor() {
-    _method.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _method);
     babelHelpers.defineProperty(this, "counter", 0);
     this.self(), 2, babelHelpers.readOnlyError("#method");
     [babelHelpers.classPrivateFieldDestructureSet(this, _method).value] = [2];
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/reassignment/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/reassignment/output.js
index d06ddb53ec..6fc9d8e6bc 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/reassignment/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/reassignment/output.js
@@ -4,8 +4,7 @@ var _privateFieldValue = /*#__PURE__*/new WeakSet();
 
 class Foo {
   constructor() {
-    _privateFieldValue.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _privateFieldValue);
     this.self, results.push(2), babelHelpers.readOnlyError("#privateFieldValue");
   }
 
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/super/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/super/output.js
index 475654149f..25ba5547ff 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/super/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/super/output.js
@@ -10,8 +10,7 @@ var _privateMethod = /*#__PURE__*/new WeakSet();
 class Sub extends Base {
   constructor(...args) {
     super(...args);
-
-    _privateMethod.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _privateMethod);
   }
 
   superMethod() {
diff --git a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/tagged-template/output.js b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/tagged-template/output.js
index 21029095ae..fb9580a3f9 100644
--- a/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/tagged-template/output.js
+++ b/packages/babel-plugin-proposal-private-methods/test/fixtures/private-method/tagged-template/output.js
@@ -2,7 +2,7 @@ var _tag = /*#__PURE__*/new WeakSet();
 
 class Foo {
   constructor() {
-    _tag.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _tag);
   }
 
 }
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private-loose/native-classes/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private-loose/native-classes/output.js
index 13ebbe4210..51e66218a8 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private-loose/native-classes/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private-loose/native-classes/output.js
@@ -2,7 +2,7 @@ var _bar = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _bar.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _bar, {
       writable: true,
       value: "bar"
     });
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/accessor/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/accessor/output.js
index 75a7587782..a5a7d2bc37 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/accessor/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/accessor/output.js
@@ -5,8 +5,7 @@ let Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       get: _get_foo,
       set: void 0
     });
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/field/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/field/output.js
index c83e48bcd8..b5206a1f38 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/field/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/field/output.js
@@ -5,8 +5,7 @@ let Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/method/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/method/output.js
index ac675cbf7d..32edd0cc6a 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/method/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/method/output.js
@@ -5,8 +5,7 @@ let Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.add(this);
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
   }
 
   babelHelpers.createClass(Foo, [{
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/native-classes/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/native-classes/output.js
index 13ebbe4210..51e66218a8 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/native-classes/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/native-classes/output.js
@@ -2,7 +2,7 @@ var _bar = /*#__PURE__*/new WeakMap();
 
 class Foo {
   constructor() {
-    _bar.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _bar, {
       writable: true,
       value: "bar"
     });
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-other-redeclared/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-other-redeclared/output.js
index a54b7a6691..82f59fa0b4 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-other-redeclared/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-other-redeclared/output.js
@@ -7,13 +7,11 @@ let Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
-
-    _bar.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _bar, {
       writable: true,
       value: 1
     });
@@ -27,8 +25,7 @@ let Foo = /*#__PURE__*/function () {
       let Nested = /*#__PURE__*/function () {
         function Nested() {
           babelHelpers.classCallCheck(this, Nested);
-
-          _bar2.set(this, {
+          babelHelpers.classPrivateFieldInitSpec(this, _bar2, {
             writable: true,
             value: 2
           });
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-redeclared/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-redeclared/output.js
index 20a7183234..b9c7cf2255 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-redeclared/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class-redeclared/output.js
@@ -5,8 +5,7 @@ let Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
@@ -20,8 +19,7 @@ let Foo = /*#__PURE__*/function () {
       let Nested = /*#__PURE__*/function () {
         function Nested() {
           babelHelpers.classCallCheck(this, Nested);
-
-          _foo2.set(this, {
+          babelHelpers.classPrivateFieldInitSpec(this, _foo2, {
             writable: true,
             value: 2
           });
diff --git a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class/output.js b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class/output.js
index 2c52c716a1..57550078e7 100644
--- a/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class/output.js
+++ b/packages/babel-plugin-proposal-private-property-in-object/test/fixtures/private/nested-class/output.js
@@ -5,8 +5,7 @@ let Foo = /*#__PURE__*/function () {
 
   function Foo() {
     babelHelpers.classCallCheck(this, Foo);
-
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: 1
     });
diff --git a/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/preset-not-loose-no-plugins/output.js b/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/preset-not-loose-no-plugins/output.js
index f3de7b04fc..e411740434 100644
--- a/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/preset-not-loose-no-plugins/output.js
+++ b/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/preset-not-loose-no-plugins/output.js
@@ -2,8 +2,7 @@ var _foo = /*#__PURE__*/new WeakSet();
 
 class A {
   constructor() {
-    _foo.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
     babelHelpers.defineProperty(this, "x", 2);
   }
 
diff --git a/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-and-methods-not-loose-preset-loose/output.js b/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-and-methods-not-loose-preset-loose/output.js
index f3de7b04fc..e411740434 100644
--- a/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-and-methods-not-loose-preset-loose/output.js
+++ b/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-and-methods-not-loose-preset-loose/output.js
@@ -2,8 +2,7 @@ var _foo = /*#__PURE__*/new WeakSet();
 
 class A {
   constructor() {
-    _foo.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
     babelHelpers.defineProperty(this, "x", 2);
   }
 
diff --git a/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-not-loose-preset-loose/output.js b/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-not-loose-preset-loose/output.js
index f3de7b04fc..e411740434 100644
--- a/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-not-loose-preset-loose/output.js
+++ b/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-not-loose-preset-loose/output.js
@@ -2,8 +2,7 @@ var _foo = /*#__PURE__*/new WeakSet();
 
 class A {
   constructor() {
-    _foo.add(this);
-
+    babelHelpers.classPrivateMethodInitSpec(this, _foo);
     babelHelpers.defineProperty(this, "x", 2);
   }
 
diff --git a/packages/babel-preset-env/test/fixtures/shipped-proposals/new-class-features-firefox-70/output.js b/packages/babel-preset-env/test/fixtures/shipped-proposals/new-class-features-firefox-70/output.js
index 458142957d..1cb775441e 100644
--- a/packages/babel-preset-env/test/fixtures/shipped-proposals/new-class-features-firefox-70/output.js
+++ b/packages/babel-preset-env/test/fixtures/shipped-proposals/new-class-features-firefox-70/output.js
@@ -2,7 +2,7 @@ var _foo = /*#__PURE__*/new WeakMap();
 
 class A {
   constructor() {
-    _foo.set(this, {
+    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
       writable: true,
       value: void 0
     });
diff --git a/packages/babel-runtime-corejs2/package.json b/packages/babel-runtime-corejs2/package.json
index 0c9b04e969..819ab3378c 100644
--- a/packages/babel-runtime-corejs2/package.json
+++ b/packages/babel-runtime-corejs2/package.json
@@ -801,6 +801,33 @@
       "./helpers/classPrivateMethodGet.js"
     ],
     "./helpers/esm/classPrivateMethodGet": "./helpers/esm/classPrivateMethodGet.js",
+    "./helpers/checkPrivateRedeclaration": [
+      {
+        "node": "./helpers/checkPrivateRedeclaration.js",
+        "import": "./helpers/esm/checkPrivateRedeclaration.js",
+        "default": "./helpers/checkPrivateRedeclaration.js"
+      },
+      "./helpers/checkPrivateRedeclaration.js"
+    ],
+    "./helpers/esm/checkPrivateRedeclaration": "./helpers/esm/checkPrivateRedeclaration.js",
+    "./helpers/classPrivateFieldInitSpec": [
+      {
+        "node": "./helpers/classPrivateFieldInitSpec.js",
+        "import": "./helpers/esm/classPrivateFieldInitSpec.js",
+        "default": "./helpers/classPrivateFieldInitSpec.js"
+      },
+      "./helpers/classPrivateFieldInitSpec.js"
+    ],
+    "./helpers/esm/classPrivateFieldInitSpec": "./helpers/esm/classPrivateFieldInitSpec.js",
+    "./helpers/classPrivateMethodInitSpec": [
+      {
+        "node": "./helpers/classPrivateMethodInitSpec.js",
+        "import": "./helpers/esm/classPrivateMethodInitSpec.js",
+        "default": "./helpers/classPrivateMethodInitSpec.js"
+      },
+      "./helpers/classPrivateMethodInitSpec.js"
+    ],
+    "./helpers/esm/classPrivateMethodInitSpec": "./helpers/esm/classPrivateMethodInitSpec.js",
     "./helpers/classPrivateMethodSet": [
       {
         "node": "./helpers/classPrivateMethodSet.js",
diff --git a/packages/babel-runtime-corejs3/package.json b/packages/babel-runtime-corejs3/package.json
index d0690a623e..8b4529b9c5 100644
--- a/packages/babel-runtime-corejs3/package.json
+++ b/packages/babel-runtime-corejs3/package.json
@@ -800,6 +800,33 @@
       "./helpers/classPrivateMethodGet.js"
     ],
     "./helpers/esm/classPrivateMethodGet": "./helpers/esm/classPrivateMethodGet.js",
+    "./helpers/checkPrivateRedeclaration": [
+      {
+        "node": "./helpers/checkPrivateRedeclaration.js",
+        "import": "./helpers/esm/checkPrivateRedeclaration.js",
+        "default": "./helpers/checkPrivateRedeclaration.js"
+      },
+      "./helpers/checkPrivateRedeclaration.js"
+    ],
+    "./helpers/esm/checkPrivateRedeclaration": "./helpers/esm/checkPrivateRedeclaration.js",
+    "./helpers/classPrivateFieldInitSpec": [
+      {
+        "node": "./helpers/classPrivateFieldInitSpec.js",
+        "import": "./helpers/esm/classPrivateFieldInitSpec.js",
+        "default": "./helpers/classPrivateFieldInitSpec.js"
+      },
+      "./helpers/classPrivateFieldInitSpec.js"
+    ],
+    "./helpers/esm/classPrivateFieldInitSpec": "./helpers/esm/classPrivateFieldInitSpec.js",
+    "./helpers/classPrivateMethodInitSpec": [
+      {
+        "node": "./helpers/classPrivateMethodInitSpec.js",
+        "import": "./helpers/esm/classPrivateMethodInitSpec.js",
+        "default": "./helpers/classPrivateMethodInitSpec.js"
+      },
+      "./helpers/classPrivateMethodInitSpec.js"
+    ],
+    "./helpers/esm/classPrivateMethodInitSpec": "./helpers/esm/classPrivateMethodInitSpec.js",
     "./helpers/classPrivateMethodSet": [
       {
         "node": "./helpers/classPrivateMethodSet.js",
diff --git a/packages/babel-runtime/package.json b/packages/babel-runtime/package.json
index c939ed29be..759a72f5b9 100644
--- a/packages/babel-runtime/package.json
+++ b/packages/babel-runtime/package.json
@@ -800,6 +800,33 @@
       "./helpers/classPrivateMethodGet.js"
     ],
     "./helpers/esm/classPrivateMethodGet": "./helpers/esm/classPrivateMethodGet.js",
+    "./helpers/checkPrivateRedeclaration": [
+      {
+        "node": "./helpers/checkPrivateRedeclaration.js",
+        "import": "./helpers/esm/checkPrivateRedeclaration.js",
+        "default": "./helpers/checkPrivateRedeclaration.js"
+      },
+      "./helpers/checkPrivateRedeclaration.js"
+    ],
+    "./helpers/esm/checkPrivateRedeclaration": "./helpers/esm/checkPrivateRedeclaration.js",
+    "./helpers/classPrivateFieldInitSpec": [
+      {
+        "node": "./helpers/classPrivateFieldInitSpec.js",
+        "import": "./helpers/esm/classPrivateFieldInitSpec.js",
+        "default": "./helpers/classPrivateFieldInitSpec.js"
+      },
+      "./helpers/classPrivateFieldInitSpec.js"
+    ],
+    "./helpers/esm/classPrivateFieldInitSpec": "./helpers/esm/classPrivateFieldInitSpec.js",
+    "./helpers/classPrivateMethodInitSpec": [
+      {
+        "node": "./helpers/classPrivateMethodInitSpec.js",
+        "import": "./helpers/esm/classPrivateMethodInitSpec.js",
+        "default": "./helpers/classPrivateMethodInitSpec.js"
+      },
+      "./helpers/classPrivateMethodInitSpec.js"
+    ],
+    "./helpers/esm/classPrivateMethodInitSpec": "./helpers/esm/classPrivateMethodInitSpec.js",
     "./helpers/classPrivateMethodSet": [
       {
         "node": "./helpers/classPrivateMethodSet.js",