diff --git a/package.json b/package.json
index 579ab000bd6..1009310efb2 100644
--- a/package.json
+++ b/package.json
@@ -3,11 +3,11 @@
   "description": "Performant, flexible and extensible forms library for React Hooks",
   "version": "7.21.0",
   "main": "dist/index.cjs.js",
-  "module": "dist/index.esm.js",
+  "module": "dist/index.esm.mjs",
   "umd:main": "dist/index.umd.js",
   "unpkg": "dist/index.umd.js",
   "jsdelivr": "dist/index.umd.js",
-  "jsnext:main": "dist/index.esm.js",
+  "jsnext:main": "dist/index.esm.mjs",
   "source": "src/index.ts",
   "types": "dist/index.d.ts",
   "sideEffects": true,
@@ -18,7 +18,7 @@
   "exports": {
     "./package.json": "./package.json",
     ".": {
-      "import": "./dist/index.esm.js",
+      "import": "./dist/index.esm.mjs",
       "require": "./dist/index.cjs.js"
     }
   },
@@ -26,7 +26,7 @@
     "clean": "rimraf dist",
     "prebuild": "yarn clean",
     "build": "yarn build:modern",
-    "postbuild": "rimraf dist/__tests__",
+    "postbuild": "rimraf dist/__tests__; node ./scripts/rollup/assert-esm-exports.mjs",
     "build:modern": "rollup -c ./scripts/rollup/rollup.config.js",
     "build:esm": "rollup -c ./scripts/rollup/rollup.esm.config.js",
     "prettier:fix": "prettier --config .prettierrc --write \"**/*.{ts,tsx}\"",
@@ -135,6 +135,6 @@
     "url": "https://opencollective.com/react-hook-form"
   },
   "engines": {
-    "node": ">=12.0"
+    "node": ">=12.22.0"
   }
 }
diff --git a/scripts/rollup/assert-esm-exports.mjs b/scripts/rollup/assert-esm-exports.mjs
new file mode 100644
index 00000000000..25fb4197621
--- /dev/null
+++ b/scripts/rollup/assert-esm-exports.mjs
@@ -0,0 +1,27 @@
+/**
+ * This file, when executed in the postbuild lifecycle, ensures that
+ * the ESM output is valid ESM according to the package.json spec.
+ *
+ * @see https://nodejs.org/docs/latest/api/packages.html#packages_determining_module_system
+ */
+import * as exported from 'react-hook-form';
+import assert from 'assert';
+
+/**
+ * A shell one-liner to update this array when neccessary:
+ *
+ *  node -e "import('react-hook-form').then((mod) => console.dir(Object.keys(mod)))"
+ */
+assert.deepStrictEqual(Object.keys(exported), [
+  'Controller',
+  'FormProvider',
+  'appendErrors',
+  'get',
+  'set',
+  'useController',
+  'useFieldArray',
+  'useForm',
+  'useFormContext',
+  'useFormState',
+  'useWatch',
+]);
diff --git a/scripts/rollup/createRollupConfig.js b/scripts/rollup/createRollupConfig.js
index 01a9eeaa691..f0b13d6e553 100644
--- a/scripts/rollup/createRollupConfig.js
+++ b/scripts/rollup/createRollupConfig.js
@@ -6,7 +6,10 @@ import typescript from 'rollup-plugin-typescript2';
 
 export function createRollupConfig(options, callback) {
   const name = options.name;
-  const outputName = 'dist/' + [name, options.format, 'js'].join('.');
+  // A file with the extension ".mjs" will always be treated as ESM, even when pkg.type is "commonjs" (the default)
+  // https://nodejs.org/docs/latest/api/packages.html#packages_determining_module_system
+  const extName = options.format === 'esm' ? 'mjs' : 'js';
+  const outputName = 'dist/' + [name, options.format, extName].join('.');
 
   const config = {
     input: options.input,