diff --git a/src/cjs/api/module-extensions.ts b/src/cjs/api/module-extensions.ts
index 4512a2568..30edd110c 100644
--- a/src/cjs/api/module-extensions.ts
+++ b/src/cjs/api/module-extensions.ts
@@ -120,6 +120,7 @@ export const createExtensions = (
 			 * If not, only expose if it's not namespaced
 			 */
 			enumerable: descriptor?.enumerable || !namespace,
+			writable: true,
 		});
 	}
 
diff --git a/tests/specs/api.ts b/tests/specs/api.ts
index 83b5133bd..afac49a70 100644
--- a/tests/specs/api.ts
+++ b/tests/specs/api.ts
@@ -79,6 +79,21 @@ export default testSuite(({ describe }, node: NodeApis) => {
 				expect(stdout).toContain('index.ts:3:22');
 			});
 
+			test('loader overwritable from Module', async () => {
+				await using fixture = await createFixture({
+					'index.mjs': `
+					import Module from 'node:module';
+					const _require = Module.createRequire(import.meta.url);
+					_require.extensions['.ts'] = () => {};
+					`,
+				});
+
+				await execaNode(fixture.getPath('index.mjs'), {
+					nodePath: node.path,
+					nodeOptions: ['--require', tsxCjsPath],
+				});
+			});
+
 			test('register / unregister', async () => {
 				await using fixture = await createFixture({
 					'register.cjs': `