diff --git a/package.json b/package.json
index 451ccd9..4145667 100644
--- a/package.json
+++ b/package.json
@@ -31,10 +31,11 @@
 		"lint": "eslint --config .configs/eslint.config.mjs .",
 		"format": "prettier --write . --config .configs/.prettierrc",
 		"format:check": "prettier --check . --config .configs/.prettierrc",
-		"test": "vitest run --config .configs/vitest.config.mjs",
+		"test": "vitest run --config .configs/vitest.config.mjs && npm run test:cjs",
+		"test:cjs": "npm run build && node --test tests/cjs/entry.test.cjs",
 		"test:watch": "vitest --config .configs/vitest.config.mjs",
-		"test:coverage": "vitest run --coverage --config .configs/vitest.config.mjs",
-		"ci:coverage": "vitest run --coverage --reporter=dot --maxWorkers=1 --config .configs/vitest.config.mjs",
+		"test:coverage": "vitest run --coverage --config .configs/vitest.config.mjs && npm run test:cjs",
+		"ci:coverage": "vitest run --coverage --reporter=dot --maxWorkers=1 --config .configs/vitest.config.mjs && npm run test:cjs",
 		"types:build": "tsc -p .configs/tsconfig.json",
 		"types:check": "tsc -p .configs/tsconfig.json --noEmit",
 		"build": "tsup",
diff --git a/src/cjs-shim.cjs b/src/cjs-shim.cjs
index bf3b04a..274890a 100644
--- a/src/cjs-shim.cjs
+++ b/src/cjs-shim.cjs
@@ -7,7 +7,7 @@
  *	@Email: <Shinrai@users.noreply.github.com>
  *	-----
  *	@Last modified by: Nate Corcoran <CLDMV> (Shinrai@users.noreply.github.com)
- *	@Last modified time: 2026-10-02T15:35:18-07:00 (1790980518)
+ *	@Last modified time: 2026-10-03T10:36:56-07:00 (1791049016)
  *	-----
  *	@Copyright: Copyright (c) 2013-2026 Catalyzed Motivation Inc. All rights reserved.
  *
@@ -21,7 +21,14 @@
  * side) as long as the target module doesn't itself use top-level await —
  * `src/runner.mjs` doesn't. This mirrors @cldmv/uuid's index.cjs pattern
  * instead of tsup bundling a second, independent copy of the whole module
- * for the CJS format.
+ * for the CJS format. In a .cjs file `require` already exists, so a plain
+ * `require("./index.mjs")` is used — `createRequire` is unnecessary here and
+ * breaks bundling by tools (esbuild/webpack) that need a static `require()`
+ * call to detect the dependency.
+ *
+ * Node.js versions without require(esm) (before 20.19 / 22.12) would fail with
+ * a bare ERR_REQUIRE_ESM, so the check below fails early with a message that
+ * says what to do instead.
  *
  * This file is copied verbatim into dist/index.cjs by tsup's onSuccess hook
  * (see tsup.config.mjs) — it never passes through esbuild itself, so it
@@ -30,7 +37,13 @@
  * @module @cldmv/vitest-runner
  */
 "use strict";
-const { createRequire } = require("node:module");
-const requireESM = createRequire(__filename);
 
-module.exports = requireESM("./index.mjs");
+if (!process.features?.require_module) {
+	const error = new Error(
+		`@cldmv/vitest-runner: require() needs Node.js ^20.19.0 or >=22.12.0 (this is ${process.version}). On older Node.js, load the package with import() instead.`
+	);
+	error.code = "ERR_REQUIRE_ESM";
+	throw error;
+}
+
+module.exports = require("./index.mjs");
diff --git a/tests/cjs/entry.test.cjs b/tests/cjs/entry.test.cjs
new file mode 100644
index 0000000..26f768c
--- /dev/null
+++ b/tests/cjs/entry.test.cjs
@@ -0,0 +1,54 @@
+/**
+ *
+ *	@Project: @cldmv/vitest-runner
+ *	@Filename: /tests/cjs/entry.test.cjs
+ *	@Date: 2026-10-03T10:33:01-07:00 (1791048781)
+ *	@Author: Nate Corcoran <CLDMV>
+ *	@Email: <Shinrai@users.noreply.github.com>
+ *	-----
+ *	@Last modified by: Nate Corcoran <CLDMV> (Shinrai@users.noreply.github.com)
+ *	@Last modified time: 2026-10-03T10:34:18-07:00 (1791048858)
+ *	-----
+ *	@Copyright: Copyright (c) 2013-2026 Catalyzed Motivation Inc. All rights reserved.
+ *
+ */
+
+/**
+ * CommonJS entry tests. These run under Node's own test runner (`node --test`), not Vitest:
+ * Vitest loads files through its own module runner, so it cannot show whether a plain
+ * `require()` of the package works the way it does for a CommonJS consumer.
+ */
+"use strict";
+
+const { test } = require("node:test");
+const assert = require("node:assert/strict");
+const { spawnSync } = require("node:child_process");
+const path = require("node:path");
+
+const repoRoot = path.resolve(__dirname, "../..");
+
+test("require() returns the same named exports as import", async () => {
+	const required = require("../../dist/index.cjs");
+	const esm = await import("../../dist/index.mjs");
+
+	assert.equal(typeof required.run, "function");
+	assert.equal(required.run, esm.run);
+	assert.equal(required.resolveBin, esm.resolveBin);
+	assert.equal(required.discoverVitestFiles, esm.discoverVitestFiles);
+	assert.equal(required.formatDuration, esm.formatDuration);
+	assert.deepEqual(Object.keys(required).sort(), Object.keys(esm).sort());
+});
+
+test("require() fails with a clear message where Node.js has no require(esm)", () => {
+	// --no-experimental-require-module turns require(esm) off, which is what Node.js
+	// versions before 20.19 / 22.12 look like to the entry.
+	const res = spawnSync(process.execPath, ["--no-experimental-require-module", "-e", "require('./dist/index.cjs')"], {
+		cwd: repoRoot,
+		encoding: "utf8"
+	});
+
+	assert.notEqual(res.status, 0);
+	assert.match(res.stderr, /ERR_REQUIRE_ESM/);
+	assert.match(res.stderr, /require\(\) needs Node\.js \^20\.19\.0 or >=22\.12\.0/);
+	assert.match(res.stderr, /import\(\)/);
+});