diff --git a/README.md b/README.md
index cd433535..e3efa858 100644
--- a/README.md
+++ b/README.md
@@ -553,7 +553,7 @@ The following table lists all the builds distributed with the `web-vitals` packa
     </td>
   </tr>
   <tr>
-    <td><code>web-vitals.umd.js</code></td>
+    <td><code>web-vitals.umd.cjs</code></td>
     <td><code>pgk.main</code></td>
     <td>
       A UMD version of the <code>web-vitals.js</code> bundle (exposed on the <code>window.webVitals.*</code> namespace).
@@ -574,7 +574,7 @@ The following table lists all the builds distributed with the `web-vitals` packa
     </td>
   </tr>
     <tr>
-    <td><code>web-vitals.attribution.umd.js</code></td>
+    <td><code>web-vitals.attribution.umd.cjs</code></td>
     <td>--</td>
     <td>
       A UMD version of the <code>web-vitals.attribution.js</code> build (exposed on the <code>window.webVitals.*</code> namespace).
@@ -598,7 +598,7 @@ The following table lists all the builds distributed with the `web-vitals` packa
     </td>
   </tr>
     <tr>
-    <td><code>web-vitals.base.umd.js</code></td>
+    <td><code>web-vitals.base.umd.cjs</code></td>
     <td>--</td>
     <td>
       <p><strong>This build has been <a href="https://github.com/GoogleChrome/web-vitals/issues/238">deprecated</a>.</strong></p>
@@ -619,7 +619,7 @@ The following table lists all the builds distributed with the `web-vitals` packa
     <td>--</td>
     <td>
       <p><strong>This build has been <a href="https://github.com/GoogleChrome/web-vitals/issues/238">deprecated</a>.</strong></p>
-      <p>The "polyfill" part of the "base+polyfill" version. This script should be used with either <code>web-vitals.base.js</code>, <code>web-vitals.base.umd.js</code>, or <code>web-vitals.base.iife.js</code> (it will not work with any script that doesn't have "base" in the filename).</p>
+      <p>The "polyfill" part of the "base+polyfill" version. This script should be used with either <code>web-vitals.base.js</code>, <code>web-vitals.base.umd.cjs</code>, or <code>web-vitals.base.iife.js</code> (it will not work with any script that doesn't have "base" in the filename).</p>
       See <a href="#how-to-use-the-polyfill">how to use the polyfill</a> for more details.
     </td>
   </tr>
diff --git a/package.json b/package.json
index 2ecdbf13..4c9029ca 100644
--- a/package.json
+++ b/package.json
@@ -4,32 +4,32 @@
   "description": "Easily measure performance metrics in JavaScript",
   "type": "module",
   "typings": "dist/modules/index.d.ts",
-  "main": "dist/web-vitals.umd.js",
+  "main": "dist/web-vitals.umd.cjs",
   "module": "dist/web-vitals.js",
   "exports": {
     ".": {
       "types": "./dist/modules/index.d.ts",
-      "require": "./dist/web-vitals.umd.js",
+      "require": "./dist/web-vitals.umd.cjs",
       "default": "./dist/web-vitals.js"
     },
     "./base": {
       "types": "./base.d.ts",
-      "require": "./dist/web-vitals.base.umd.js",
+      "require": "./dist/web-vitals.base.umd.cjs",
       "default": "./dist/web-vitals.base.js"
     },
     "./base.js": {
       "types": "./base.d.ts",
-      "require": "./dist/web-vitals.base.umd.js",
+      "require": "./dist/web-vitals.base.umd.cjs",
       "default": "./dist/web-vitals.base.js"
     },
     "./attribution": {
       "types": "./dist/modules/attribution.d.ts",
-      "require": "./dist/web-vitals.attribution.umd.js",
+      "require": "./dist/web-vitals.attribution.umd.cjs",
       "default": "./dist/web-vitals.attribution.js"
     },
     "./attribution.js": {
       "types": "./dist/modules/attribution.d.ts",
-      "require": "./dist/web-vitals.attribution.umd.js",
+      "require": "./dist/web-vitals.attribution.umd.cjs",
       "default": "./dist/web-vitals.attribution.js"
     },
     "./onCLS.js": {
diff --git a/rollup.config.js b/rollup.config.js
index 7964a78a..087c6c80 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -53,7 +53,7 @@ const configs = [
     input: 'dist/modules/index.js',
     output: {
       format: 'umd',
-      file: `./dist/web-vitals.umd.js`,
+      file: `./dist/web-vitals.umd.cjs`,
       name: 'webVitals',
     },
     plugins: configurePlugins({module: false, polyfill: false}),
@@ -79,7 +79,7 @@ const configs = [
     input: 'dist/modules/index.js',
     output: {
       format: 'umd',
-      file: `./dist/web-vitals.base.umd.js`,
+      file: `./dist/web-vitals.base.umd.cjs`,
       name: 'webVitals',
       extend: true,
     },
@@ -117,7 +117,7 @@ const configs = [
     input: 'dist/modules/attribution.js',
     output: {
       format: 'umd',
-      file: `./dist/web-vitals.attribution.umd.js`,
+      file: `./dist/web-vitals.attribution.umd.cjs`,
       name: 'webVitals',
     },
     plugins: configurePlugins({module: false, polyfill: false}),