diff --git a/lib/6to5/transformation/transformers/optional-core-aliasing.js b/lib/6to5/transformation/transformers/optional-core-aliasing.js
index c0db8bd9bd..62613bf198 100644
--- a/lib/6to5/transformation/transformers/optional-core-aliasing.js
+++ b/lib/6to5/transformation/transformers/optional-core-aliasing.js
@@ -23,7 +23,7 @@ exports.optional = true;
 
 exports.ast = {
   enter: function (ast, file) {
-    file._coreId = file.addImport("core-js/library", "core");
+    file._coreId = file.addImport("6to5-runtime/core-js", "core");
   },
 
   exit: function (ast, file) {
diff --git a/lib/6to5/transformation/transformers/optional-external-regenerator-runtime.js b/lib/6to5/transformation/transformers/optional-external-regenerator-runtime.js
index 9294a6c76e..6fee6be612 100644
--- a/lib/6to5/transformation/transformers/optional-external-regenerator-runtime.js
+++ b/lib/6to5/transformation/transformers/optional-external-regenerator-runtime.js
@@ -4,7 +4,7 @@ exports.optional = true;
 
 exports.ast = {
   enter: function (ast, file) {
-    file._regeneratorId = file.addImport("regenerator/runtime-module", "regeneratorRuntime");
+    file._regeneratorId = file.addImport("6to5-runtime/regenerator", "regeneratorRuntime");
   }
 };
 
diff --git a/lib/6to5/transformation/transformers/optional-external-runtime.js b/lib/6to5/transformation/transformers/optional-external-runtime.js
index ff39454e4d..56c14e0fc4 100644
--- a/lib/6to5/transformation/transformers/optional-external-runtime.js
+++ b/lib/6to5/transformation/transformers/optional-external-runtime.js
@@ -5,6 +5,6 @@ exports.optional = true;
 // AST is built.
 exports.ast = {
   enter: function (ast, file) {
-    file.opts.runtime = file.addImport(file.opts.runtime, "to5Runtime").name;
+    file.opts.runtime = file.addImport("6to5-runtime/6to5", "to5Runtime").name;
   }
 };
diff --git a/test/fixtures/transformation/optional-core-aliasing/aliased-constructors/expected.js b/test/fixtures/transformation/optional-core-aliasing/aliased-constructors/expected.js
index 8c6ff60ed1..b517b90ea6 100644
--- a/test/fixtures/transformation/optional-core-aliasing/aliased-constructors/expected.js
+++ b/test/fixtures/transformation/optional-core-aliasing/aliased-constructors/expected.js
@@ -1,6 +1,6 @@
 "use strict";
 
-var _core = require("core-js/library");
+var _core = require("6to5-runtime/core-js");
 
 obj.constructor === Object;
 obj.constructor === _core.Promise;
diff --git a/test/fixtures/transformation/optional-core-aliasing/es6-destructuring/expected.js b/test/fixtures/transformation/optional-core-aliasing/es6-destructuring/expected.js
index 15e3ce78b9..7abd2c0cd5 100644
--- a/test/fixtures/transformation/optional-core-aliasing/es6-destructuring/expected.js
+++ b/test/fixtures/transformation/optional-core-aliasing/es6-destructuring/expected.js
@@ -16,7 +16,7 @@ var _slicedToArray = function (arr, i) {
   }
 };
 
-var _core = require("core-js/library");
+var _core = require("6to5-runtime/core-js");
 
 var _ref = ["hello", [", ", "junk"], ["world"]];
 
diff --git a/test/fixtures/transformation/optional-core-aliasing/es6-for-of/expected.js b/test/fixtures/transformation/optional-core-aliasing/es6-for-of/expected.js
index 2669fd4d0c..0fdc4cc4f5 100644
--- a/test/fixtures/transformation/optional-core-aliasing/es6-for-of/expected.js
+++ b/test/fixtures/transformation/optional-core-aliasing/es6-for-of/expected.js
@@ -1,6 +1,6 @@
 "use strict";
 
-var _core = require("core-js/library");
+var _core = require("6to5-runtime/core-js");
 
 for (var _iterator = _core.$for.getIterator(arr), _step; !(_step = _iterator.next()).done;) {
   var i = _step.value;
diff --git a/test/fixtures/transformation/optional-core-aliasing/es6-spread/expected.js b/test/fixtures/transformation/optional-core-aliasing/es6-spread/expected.js
index 2a41ccd997..d01fa15ace 100644
--- a/test/fixtures/transformation/optional-core-aliasing/es6-spread/expected.js
+++ b/test/fixtures/transformation/optional-core-aliasing/es6-spread/expected.js
@@ -4,6 +4,6 @@ var _toArray = function (arr) {
   return Array.isArray(arr) ? arr : _core.Array.from(arr);
 };
 
-var _core = require("core-js/library");
+var _core = require("6to5-runtime/core-js");
 
 var lyrics = ["head", "and", "toes"].concat(_toArray(parts));
diff --git a/test/fixtures/transformation/optional-core-aliasing/es7-array-comprehensions/expected.js b/test/fixtures/transformation/optional-core-aliasing/es7-array-comprehensions/expected.js
index 0bf67a612a..9ea3b708c6 100644
--- a/test/fixtures/transformation/optional-core-aliasing/es7-array-comprehensions/expected.js
+++ b/test/fixtures/transformation/optional-core-aliasing/es7-array-comprehensions/expected.js
@@ -1,6 +1,6 @@
 "use strict";
 
-var _core = require("core-js/library");
+var _core = require("6to5-runtime/core-js");
 
 var arr = (function () {
   var _arr = [];
diff --git a/test/fixtures/transformation/optional-external-regenerator-runtime/basic/expected.js b/test/fixtures/transformation/optional-external-regenerator-runtime/basic/expected.js
index 00320c54b6..275ec24ac5 100644
--- a/test/fixtures/transformation/optional-external-regenerator-runtime/basic/expected.js
+++ b/test/fixtures/transformation/optional-external-regenerator-runtime/basic/expected.js
@@ -1,6 +1,6 @@
 "use strict";
 
-var _regeneratorRuntime = require("regenerator/runtime-module");
+var _regeneratorRuntime = require("6to5-runtime/regenerator");
 
 void _regeneratorRuntime.mark(function callee$0$0() {
   return _regeneratorRuntime.wrap(function callee$0$0$(context$1$0) {
diff --git a/test/fixtures/transformation/optional-external-runtime/amd/expected.js b/test/fixtures/transformation/optional-external-runtime/amd/expected.js
index 20e759af12..6e504dd685 100644
--- a/test/fixtures/transformation/optional-external-runtime/amd/expected.js
+++ b/test/fixtures/transformation/optional-external-runtime/amd/expected.js
@@ -1,6 +1,6 @@
-define(["exports", "6to5-runtime", "someModule"], function (exports, _to5Runtime2, _someModule) {
+define(["exports", "6to5-runtime/6to5", "someModule"], function (exports, _to5Runtime6to5, _someModule) {
   "use strict";
 
-  var _to5Runtime = _to5Runtime2;
+  var _to5Runtime = _to5Runtime6to5;
   var foo = _to5Runtime.interopRequire(_someModule);
 });
diff --git a/test/fixtures/transformation/optional-external-runtime/commonjs/expected.js b/test/fixtures/transformation/optional-external-runtime/commonjs/expected.js
index b10bbe6f09..d660411bc0 100644
--- a/test/fixtures/transformation/optional-external-runtime/commonjs/expected.js
+++ b/test/fixtures/transformation/optional-external-runtime/commonjs/expected.js
@@ -1,5 +1,5 @@
 "use strict";
 
-var _to5Runtime = require("6to5-runtime");
+var _to5Runtime = require("6to5-runtime/6to5");
 
 var foo = _to5Runtime.interopRequireWildcard(require("someModule"));
diff --git a/test/fixtures/transformation/optional-external-runtime/options.json b/test/fixtures/transformation/optional-external-runtime/options.json
index 44c5164a67..5149c1159a 100644
--- a/test/fixtures/transformation/optional-external-runtime/options.json
+++ b/test/fixtures/transformation/optional-external-runtime/options.json
@@ -1,4 +1,3 @@
 {
-  "runtime": "6to5-runtime",
   "optional": ["externalRuntime"]
 }