diff --git a/lib/micromark.mjs b/lib/micromark.cjs
similarity index 90%
rename from lib/micromark.mjs
rename to lib/micromark.cjs
index d0f1ec20..5b7bb5d3 100644
--- a/lib/micromark.mjs
+++ b/lib/micromark.cjs
@@ -1,12 +1,12 @@
 // @ts-check
 
-/* eslint-disable n/no-unpublished-import */
+"use strict";
 
-import assert from "node:assert/strict";
+/* eslint-disable n/no-unpublished-require */
+
+const assert = require("node:assert/strict");
 // @ts-ignore
-import micromark from "../micromark/micromark.js";
-// @ts-ignore
-const { parse, postprocess, preprocess } = micromark;
+const { parse, postprocess, preprocess } = require("../micromark/micromark.js");
 
 /**
  * Markdown token.
@@ -84,6 +84,6 @@ function micromarkParse(markdown) {
   return document;
 }
 
-export {
-  micromarkParse as parse
+module.exports = {
+  "parse": micromarkParse
 };
diff --git a/test/markdownlint-test-micromark.mjs b/test/markdownlint-test-micromark.mjs
index fe4fa1e5..96111414 100644
--- a/test/markdownlint-test-micromark.mjs
+++ b/test/markdownlint-test-micromark.mjs
@@ -3,7 +3,7 @@
 import fs from "node:fs/promises";
 import test from "ava";
 import { newLineRe } from "../helpers/helpers.js";
-import { parse } from "../lib/micromark.mjs";
+import { parse } from "../lib/micromark.cjs";
 
 test("parse", async(t) => {
   t.plan(1);