diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d810b0a6333e..71937c8a1210 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -8,10 +8,10 @@ Contributions are always welcome. If you don't know how you can help, you can ch
 - Any shared helpers should be added to the [`packages/core-js/internals`](./packages/core-js/internals) directory.
 - If the implementation for the `pure` version differs from the global version, add it to [`packages/core-js-pure/override`](./packages/core-js-pure/override) directory. The rest parts of `core-js-pure` will be copied from `core-js` package.
 - For export the polyfill, in almost all cases use `internals/export` helper.
-- Add feature detection of the polyfill to [`tests/compat/tests.js`](./tests/compat/tests.js) and compatibility data to [`packages/core-js-compat/src/data.js`](./packages/core-js-compat/src/data.js) and [`packages/core-js-compat/src/modules-by-versions.js`](./packages/core-js-compat/src/modules-by-versions.js) (this data also used for getting the default list of polyfills at bundling).
+- Add feature detection of the polyfill to [`tests/compat/tests.js`](./tests/compat/tests.js) and compatibility data to [`packages/core-js-compat/src/data.mjs`](./packages/core-js-compat/src/data.mjs) and [`packages/core-js-compat/src/modules-by-versions.mjs`](./packages/core-js-compat/src/modules-by-versions.mjs) (this data also used for getting the default list of polyfills at bundling).
 - Add it to entry points where it's required: directories [`packages/core-js/features`](./packages/core-js/features), [`packages/core-js/es`](./packages/core-js/es), [`packages/core-js/proposals`](./packages/core-js/proposals), [`packages/core-js/stage`](./packages/core-js/stage) and [`packages/core-js/web`](./packages/core-js/web).
 - Add unit tests to [`tests/tests`](./tests/tests) and [`tests/pure`](./tests/pure).
-- Add tests of entry points to [`tests/commonjs.js`](./tests/commonjs).
+- Add tests of entry points to [`tests/commonjs.js`](./tests/commonjs.js).
 - Add documentation to [README.md](./README.md).
 
 ## Style and standards
@@ -78,6 +78,6 @@ For updating `core-js-compat` data:
 - Clone `core-js` repo.
 - If you wanna add new data for a browser, run in this browser `tests/compat/index.html` and you will see which `core-js` modules required for this browser.
 - If you wanna add new data for Node.js, run `tests/compat/node-runner.js` in required Node.js version and you will see results in the console.
-- After getting this data, add it to [`packages/core-js-compat/src/data.js`](./packages/core-js-compat/src/data.js).
-- If you wanna add new mapping (for example, add a new iOS Safari version based on Safari or Node.js based on Chrome), add it to [`packages/core-js-compat/src/mapping.js`](./packages/core-js-compat/src/mapping.js).
+- After getting this data, add it to [`packages/core-js-compat/src/data.mjs`](./packages/core-js-compat/src/data.mjs).
+- If you wanna add new mapping (for example, add a new iOS Safari version based on Safari or Node.js based on Chrome), add it to [`packages/core-js-compat/src/mapping.mjs`](./packages/core-js-compat/src/mapping.mjs).
 - Add a pull request to `core-js` repo.