diff --git a/lib/index.js b/lib/index.cjs
similarity index 100%
rename from lib/index.js
rename to lib/index.cjs
diff --git a/lib/index.test.js b/lib/index.test.js
index 1128489..65b3010 100644
--- a/lib/index.test.js
+++ b/lib/index.test.js
@@ -40,7 +40,7 @@ describe('format', () => {
       Promise.resolve(
         prettier.format(uglyJson, {
           filepath: 'package.json',
-          plugins: ['./lib/index.js'],
+          plugins: ['./lib/index.cjs'],
         }),
       ),
     ).resolves.toMatchSnapshot())
@@ -51,7 +51,7 @@ describe('format', () => {
         prettier.format(uglyJson, {
           parser: 'json-stringify',
           filepath: 'foo.json',
-          plugins: ['./lib/index.js'],
+          plugins: ['./lib/index.cjs'],
         }),
       ),
     ).resolves.toBe(uglyJson))
@@ -64,7 +64,7 @@ describe('format', () => {
       Promise.resolve(
         prettier.format(uglyJson, {
           filepath: 'package.json',
-          plugins: ['./lib/index.js'],
+          plugins: ['./lib/index.cjs'],
         }),
       ),
     ).resolves.toBe('{}\n')
diff --git a/package.json b/package.json
index 9ac693a..2f607fb 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
   ],
   "repository": "github:matzkoh/prettier-plugin-packagejson",
   "license": "MIT",
-  "main": "lib",
+  "main": "lib/index.cjs",
   "directories": {
     "lib": "lib"
   },
diff --git a/prettier.config.js b/prettier.config.cjs
similarity index 83%
rename from prettier.config.js
rename to prettier.config.cjs
index 0585ffd..55e174c 100644
--- a/prettier.config.js
+++ b/prettier.config.cjs
@@ -5,5 +5,5 @@ module.exports = {
   semi: false,
   singleQuote: true,
   trailingComma: 'all',
-  plugins: ['./lib/index.js'],
+  plugins: ['./lib/index.cjs'],
 }