diff --git a/index.js b/index.js
index e1791a9..7827409 100644
--- a/index.js
+++ b/index.js
@@ -206,6 +206,10 @@ function css(css, file) {
         )
       }
 
+      if (!options.parser && !options.syntax && !options.stringifier) {
+        options.syntax = require('postcss-syntax')
+      }
+
       return postcss(config.plugins)
         .process(css, options)
         .then(result => {
diff --git a/package.json b/package.json
index 2f5f8cb..5c8df49 100644
--- a/package.json
+++ b/package.json
@@ -27,6 +27,7 @@
     "postcss": "^6.0.1",
     "postcss-load-config": "^1.1.0",
     "postcss-reporter": "^5.0.0",
+    "postcss-syntax": "^0.1.0",
     "pretty-hrtime": "^1.0.3",
     "read-cache": "^1.0.0",
     "yargs": "^11.0.0"
diff --git a/test/syntax.js b/test/syntax.js
index 39877d8..a73f554 100644
--- a/test/syntax.js
+++ b/test/syntax.js
@@ -20,3 +20,19 @@ test('--syntax works', async t => {
 
   t.is(await read(output), await read('test/fixtures/a.sss'))
 })
+
+test('automatically switch syntax', async t => {
+  const dir = tmp()
+
+  const { error, stderr } = await cli([
+    'test/fixtures/b.*',
+    '-d',
+    dir,
+    '--no-map'
+  ])
+
+  t.ifError(error, stderr)
+
+  t.is(await read(`${dir}/b.sss`), await read('test/fixtures/b.sss'))
+  t.is(await read(`${dir}/b.css`), await read('test/fixtures/b.css'))
+})