diff --git a/package.json b/package.json
index 5d03ab5..2ec64d3 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "MessagePack for ECMA-262/JavaScript/TypeScript",
   "author": "The MessagePack community",
   "license": "ISC",
-  "main": "./dist.cjs/index.js",
+  "main": "./dist.cjs/index.cjs",
   "module": "./dist.esm/index.mjs",
   "cdn": "./dist.umd/msgpack.min.js",
   "unpkg": "./dist.umd/msgpack.min.js",
@@ -12,13 +12,13 @@
   "sideEffects": false,
   "scripts": {
     "build": "npm publish --dry-run",
-    "prepare": "npm run clean && webpack --bail && tsc --build tsconfig.dist.cjs.json tsconfig.dist.esm.json && ts-node tools/esmify.ts dist.esm/*.js dist.esm/*/*.js",
+    "prepare": "npm run clean && webpack --bail && tsc --build tsconfig.dist.cjs.json tsconfig.dist.esm.json && tsimp tools/fix-ext.mts --mjs dist.esm/*.js dist.esm/*/*.js && tsimp tools/fix-ext.mts --cjs dist.cjs/*.js dist.cjs/*/*.js",
     "prepublishOnly": "npm run test:dist",
     "clean": "rimraf build dist dist.*",
     "test": "mocha 'test/**/*.test.ts'",
     "test:dist": "npm run lint && npm run test && npm run test:deno",
     "test:cover": "npm run cover:clean && npx nyc --no-clean npm run 'test' && npm run cover:report",
-    "test:deno": "deno test test/deno_test.ts",
+    "test:deno": "deno test --allow-read test/deno_*.ts",
     "test:bun": "bun test test/bun.spec.ts",
     "test:fuzz": "npm exec --yes -- jsfuzz@git+https://gitlab.com/gitlab-org/security-products/analyzers/fuzzers/jsfuzz.git#39e6cf16613a0e30c7a7953f62e64292dbd5d3f3 --fuzzTime 60 --no-versifier test/decode.jsfuzz.js corpus",
     "cover:clean": "rimraf .nyc_output coverage/",
@@ -89,10 +89,10 @@
     "webpack-cli": "latest"
   },
   "files": [
-    "mod.ts",
     "src/**/*.*",
-    "dist/**/*.*",
+    "dist.cjs/**/*.*",
+    "dist.esm/**/*.*",
     "dist.umd/**/*.*",
-    "dist.esm/**/*.*"
+    "mod.ts"
   ]
 }
diff --git a/test/deno_cjs_test.ts b/test/deno_cjs_test.ts
new file mode 100755
index 0000000..7293f0a
--- /dev/null
+++ b/test/deno_cjs_test.ts
@@ -0,0 +1,12 @@
+#!/usr/bin/env deno test --allow-read
+
+/* eslint-disable */
+import { deepStrictEqual } from "node:assert";
+import { test } from "node:test";
+import * as msgpack from "../dist.cjs/index.cjs";
+
+test("Hello, world!", () => {
+  const encoded = msgpack.encode("Hello, world!");
+  const decoded = msgpack.decode(encoded);
+  deepStrictEqual(decoded, "Hello, world!");
+});
diff --git a/tools/esmify.ts b/tools/esmify.ts
deleted file mode 100644
index 8447c10..0000000
--- a/tools/esmify.ts
+++ /dev/null
@@ -1,25 +0,0 @@
-#!ts-node
-/* eslint-disable no-console */
-
-import fs from "fs";
-
-const files = process.argv.slice(2);
-
-for (const file of files) {
-  const fileMjs = file.replace(/\.js$/, ".mjs");
-  console.info(`Processing ${file} => ${fileMjs}`);
-  // .js => .mjs
-  const content = fs.readFileSync(file).toString("utf-8");
-  const newContent = content.replace(/\bfrom "(\.\.?\/[^"]+)";/g, 'from "$1.mjs";')
-    .replace(/\bimport "(\.\.?\/[^"]+)";/g, 'import "$1.mjs";')
-    .replace(/\/\/# sourceMappingURL=(.+)\.js\.map$/,
-      "//# sourceMappingURL=$1.mjs.map");
-  fs.writeFileSync(fileMjs, newContent);
-  fs.unlinkSync(file);
-
-  // .js.map => .mjs.map
-  const mapping = JSON.parse(fs.readFileSync(`${file}.map`).toString("utf-8"));
-  mapping.file = mapping.file.replace(/\.js$/, ".mjs");
-  fs.writeFileSync(`${fileMjs}.map`, JSON.stringify(mapping));
-  fs.unlinkSync(`${file}.map`);
-}
diff --git a/tools/fix-ext.mts b/tools/fix-ext.mts
new file mode 100644
index 0000000..80250bc
--- /dev/null
+++ b/tools/fix-ext.mts
@@ -0,0 +1,28 @@
+import fs from "node:fs";
+
+const mode = process.argv[2]; // --cjs or --mjs
+const files = process.argv.slice(3);
+
+const ext = mode === "--cjs" ? "cjs" : "mjs";
+
+console.info(`Fixing ${mode} files with extension ${ext}`);
+
+for (const file of files) {
+  const fileMjs = file.replace(/\.js$/, `.${ext}`);
+  console.info(`Processing ${file} => ${fileMjs}`);
+  // .js => .mjs
+  const content = fs.readFileSync(file).toString("utf-8");
+  const newContent = content
+    .replace(/\bfrom "(\.\.?\/[^"]+)(?:\.js)?";/g, `from "$1.${ext}";`)
+    .replace(/\bimport "(\.\.?\/[^"]+)(?:\.js)?";/g, `import "$1.${ext}";`)
+    .replace(/\brequire\("(\.\.?\/[^"]+)(?:\.js)?"\)/g, `require("$1.${ext}");`)
+    .replace(/\/\/# sourceMappingURL=(.+)\.js\.map$/, `//# sourceMappingURL=$1.${ext}.map`);
+  fs.writeFileSync(fileMjs, newContent);
+  fs.unlinkSync(file);
+
+  // .js.map => .mjs.map
+  const mapping = JSON.parse(fs.readFileSync(`${file}.map`).toString("utf-8"));
+  mapping.file = mapping.file.replace(/\.js$/, ext);
+  fs.writeFileSync(`${fileMjs}.map`, JSON.stringify(mapping));
+  fs.unlinkSync(`${file}.map`);
+}