diff --git a/test/config.js b/test/config.js
index 7666b83..bb32d97 100644
--- a/test/config.js
+++ b/test/config.js
@@ -5,6 +5,7 @@ import ENV from './helpers/env.js'
 
 import cli from './helpers/cli.js'
 import read from './helpers/read.js'
+import tmp from './helpers/tmp.js'
 
 test('supports common config', async (t) => {
   const env = `module.exports = {
@@ -13,10 +14,10 @@ test('supports common config', async (t) => {
     ]
   }`
 
-  const dir = await ENV(env, ['a.css'])
+  const dir = await ENV(env, ['import.css', 'a.css'])
 
   const { error, stderr } = await cli(
-    ['a.css', '-o', 'output.css', '--no-map'],
+    ['import.css', '-o', 'output.css', '--no-map'],
     dir,
   )
 
@@ -38,10 +39,10 @@ test('supports ESM config', async (t) => {
     }
   }`
 
-  const dir = await ENV(env, ['a.css'], 'mjs')
+  const dir = await ENV(env, ['import.css', 'a.css'], 'mjs')
 
   const { error, stderr } = await cli(
-    ['a.css', '-o', 'output.css', '--no-map'],
+    ['import.css', '-o', 'output.css', '--no-map'],
     dir,
   )
 
@@ -100,3 +101,20 @@ test('errors if `from` is set', async (t) => {
     /Config Error: Can not set from or to options in config file, use CLI arguments instead/,
   )
 })
+
+test('supports --config flag', async (t) => {
+  const output = tmp('output.css')
+
+  const { error, stderr } = await cli([
+    'test/fixtures/import.css',
+    '-o',
+    output,
+    '--no-map',
+    '--config',
+    'test/fixtures/cfg-dir',
+  ])
+
+  t.falsy(error, stderr)
+
+  t.is(await read(output), await read('test/fixtures/a.css'))
+})
diff --git a/test/fixtures/cfg-dir/postcss.config.js b/test/fixtures/cfg-dir/postcss.config.js
new file mode 100644
index 0000000..e9c454b
--- /dev/null
+++ b/test/fixtures/cfg-dir/postcss.config.js
@@ -0,0 +1,6 @@
+import postcssImport from 'postcss-import'
+export default function () {
+  return {
+    plugins: [postcssImport()],
+  }
+}