diff --git a/test/config.js b/test/config.js
index a4eb8c6..d75449c 100644
--- a/test/config.js
+++ b/test/config.js
@@ -28,6 +28,31 @@ test('supports common config', async (t) => {
   )
 })
 
+test('supports ESM config', async (t) => {
+  const env = `import postcssImport from 'postcss-import'
+  export default function () {
+    return {
+      plugins: [
+        postcssImport()
+      ]
+    }
+  }`
+
+  const dir = await ENV(env, ['a.css'], 'mjs')
+
+  const { error, stderr } = await cli(
+    ['a.css', '-o', 'output.css', '--no-map'],
+    dir
+  )
+
+  t.falsy(error, stderr)
+
+  t.is(
+    await read(path.join(dir, 'output.css')),
+    await read('test/fixtures/a.css')
+  )
+})
+
 test("doesn't error on empty config", async (t) => {
   const env = `module.exports = {}`
 
diff --git a/test/helpers/env.js b/test/helpers/env.js
index 7ec542e..dfdba26 100644
--- a/test/helpers/env.js
+++ b/test/helpers/env.js
@@ -4,8 +4,7 @@ import { globby } from 'globby'
 
 import tmp from './tmp.js'
 
-export default function (config, fixtures) {
-  fixtures = fixtures || '**/*'
+export default function (config, fixtures = '**/*', extension = 'cjs') {
   const dir = tmp()
 
   return Promise.all([
@@ -14,6 +13,6 @@ export default function (config, fixtures) {
         return fs.copy(path.join('test/fixtures', item), path.join(dir, item))
       })
     }),
-    fs.outputFile(path.join(dir, 'postcss.config.cjs'), config),
+    fs.outputFile(path.join(dir, `postcss.config.${extension}`), config),
   ]).then(() => dir)
 }