diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index da16f07..a85cce4 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -145,7 +145,7 @@ jobs:
         run: yarn test
         if: matrix.example != 'are-the-types-wrong'
 
-      - name: Run test step
+      - name: Run test step (attw)
         working-directory: ./redux-toolkit/examples/publish-ci/${{ matrix.example }}
         # Ignore "FalseCJS" errors in the `attw` job
         run: yarn test -n FalseCJS
diff --git a/package.json b/package.json
index 4f2277f..bcaae10 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,7 @@
   ],
   "author": "Dan Abramov <dan.abramov@me.com>",
   "main": "dist/cjs/redux-thunk.cjs",
-  "module": "dist/redux-thunk.mjs",
+  "module": "dist/redux-thunk.legacy-esm.js",
   "types": "dist/redux-thunk.d.ts",
   "exports": {
     "./package.json": "./package.json",
diff --git a/tsup.config.ts b/tsup.config.ts
index fe3e25e..22b3528 100644
--- a/tsup.config.ts
+++ b/tsup.config.ts
@@ -1,4 +1,5 @@
 import { defineConfig, Options } from 'tsup'
+import fs from 'fs'
 
 export default defineConfig(options => {
   const commonOptions: Partial<Options> = {
@@ -14,7 +15,14 @@ export default defineConfig(options => {
       format: ['esm'],
       outExtension: () => ({ js: '.mjs' }),
       dts: true,
-      clean: true
+      clean: true,
+      onSuccess() {
+        // Support Webpack 4 by pointing `"module"` to a file with a `.js` extension
+        fs.copyFileSync(
+          'dist/redux-thunk.mjs',
+          'dist/redux-thunk.legacy-esm.js'
+        )
+      }
     },
     {
       ...commonOptions,