diff --git a/packages/babel-helper-member-expression-to-functions/package.json b/packages/babel-helper-member-expression-to-functions/package.json
index 51ce3de0b0..635b5fe628 100644
--- a/packages/babel-helper-member-expression-to-functions/package.json
+++ b/packages/babel-helper-member-expression-to-functions/package.json
@@ -16,5 +16,8 @@
   "author": "Justin Ridgewell <justin@ridgewell.name>",
   "dependencies": {
     "@babel/types": "workspace:^7.13.0"
+  },
+  "devDependencies": {
+    "@babel/traverse": "workspace:^7.12.17"
   }
 }
diff --git a/packages/babel-helper-member-expression-to-functions/src/index.js b/packages/babel-helper-member-expression-to-functions/src/index.ts
similarity index 97%
rename from packages/babel-helper-member-expression-to-functions/src/index.js
rename to packages/babel-helper-member-expression-to-functions/src/index.ts
index 52a28e8de3..6cdddbefb2 100644
--- a/packages/babel-helper-member-expression-to-functions/src/index.js
+++ b/packages/babel-helper-member-expression-to-functions/src/index.ts
@@ -2,6 +2,7 @@ import * as t from "@babel/types";
 import { willPathCastToBoolean } from "./util";
 
 class AssignmentMemoiser {
+  private _map: WeakMap<object, any>;
   constructor() {
     this._map = new WeakMap();
   }
@@ -84,7 +85,8 @@ const handle = {
     // noop.
   },
 
-  handle(member: t.NodePath<t.Expression>, noDocumentAll: boolean) {
+  // todo(flow->ts) member:NodePath<t.Expression>, refactor function body to avoid too many typecasts
+  handle(member: any, noDocumentAll: boolean) {
     const { node, parent, parentPath, scope } = member;
 
     if (member.isOptionalMemberExpression()) {
@@ -350,7 +352,12 @@ const handle = {
         const ref = scope.generateUidIdentifierBasedOnNode(node);
         scope.push({ id: ref });
 
-        value.left = t.assignmentExpression("=", t.cloneNode(ref), value.left);
+        value.left = t.assignmentExpression(
+          "=",
+          t.cloneNode(ref),
+          // @ts-expect-error todo(flow->ts) value.left is possibly PrivateName, which is not usable here
+          value.left,
+        );
 
         parentPath.replaceWith(
           t.sequenceExpression([this.set(member, value), t.cloneNode(ref)]),
diff --git a/packages/babel-helper-member-expression-to-functions/src/util.js b/packages/babel-helper-member-expression-to-functions/src/util.ts
similarity index 96%
rename from packages/babel-helper-member-expression-to-functions/src/util.js
rename to packages/babel-helper-member-expression-to-functions/src/util.ts
index 107ff410eb..0c77683e4f 100644
--- a/packages/babel-helper-member-expression-to-functions/src/util.js
+++ b/packages/babel-helper-member-expression-to-functions/src/util.ts
@@ -1,3 +1,5 @@
+import type { NodePath } from "@babel/traverse";
+
 /**
  * Test if a NodePath will be cast to boolean when evaluated.
  *
diff --git a/yarn.lock b/yarn.lock
index 3760fee11b..59d3a43e96 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -621,6 +621,7 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@babel/helper-member-expression-to-functions@workspace:packages/babel-helper-member-expression-to-functions"
   dependencies:
+    "@babel/traverse": "workspace:^7.12.17"
     "@babel/types": "workspace:^7.13.0"
   languageName: unknown
   linkType: soft