diff --git a/src/index.js b/src/index.js
index 2038b925..bd3f3e51 100644
--- a/src/index.js
+++ b/src/index.js
@@ -108,9 +108,10 @@ export default (options = {}) => {
             filepath = postcssLoaderOptions.extract
           } else {
             const basename = path.basename(opts.file, path.extname(opts.file))
-            filepath = normalizePath(path.join(path.dirname(opts.file), basename + '.css'))
+            filepath = path.join(path.dirname(opts.file), basename + '.css')
           }
         }
+        filepath = normalizePath(filepath)
         const concat = new Concat(true, filepath, '\n')
         for (const res of extracted) {
           const relative = normalizePath(res.id)
diff --git a/test/__snapshots__/index.test.js.snap b/test/__snapshots__/index.test.js.snap
index 5504a11a..831abc9a 100644
--- a/test/__snapshots__/index.test.js.snap
+++ b/test/__snapshots__/index.test.js.snap
@@ -123,7 +123,7 @@ body {
 /*# sourceMappingURL=extracted.css.map */"
 `;
 
-exports[`extract:path: css map 1`] = `"{\\"version\\":3,\\"sources\\":[\\"test/fixtures/dist/extract:path/foo.css\\",\\"test/fixtures/dist/extract:path/bar.css\\",\\"test/fixtures/dist/extract:path/test/fixtures/simple/style.styl\\",\\"test/fixtures/dist/extract:path/style.styl\\",\\"test/fixtures/dist/extract:path/style.sass\\",\\"test/fixtures/dist/extract:path/input\\",\\"test/fixtures/dist/extract:path/style.less\\"],\\"names\\":[],\\"mappings\\":\\"AAAA;EACE,WAAW;CACZ;;ACFD;EACE,WAAW;CACZ;;ACFD;EACE,YAAA;EACA,iBAAA;CCCD;AACD,0DAA0D;ACJ1D;EACE,WAAW;EACX,uBAAuB,EAAE;;ACC3B;EACE,eAAA;CCFD\\",\\"file\\":\\"/Users/egoist/dev/rollup-plugin-postcss/test/fixtures/dist/extract:path/this/is/extracted.css\\",\\"sourcesContent\\":[\\"body {\\\\n  color: red;\\\\n}\\\\n\\",\\".bar {\\\\n  color: red;\\\\n}\\\\n\\",null,null,\\"#sidebar {\\\\n  width: 30%;\\\\n  background-color: #faa; }\\\\n\\",null,null]}"`;
+exports[`extract:path: css map 1`] = `"{\\"version\\":3,\\"sources\\":[\\"test/fixtures/dist/extract:path/foo.css\\",\\"test/fixtures/dist/extract:path/bar.css\\",\\"test/fixtures/dist/extract:path/test/fixtures/simple/style.styl\\",\\"test/fixtures/dist/extract:path/style.styl\\",\\"test/fixtures/dist/extract:path/style.sass\\",\\"test/fixtures/dist/extract:path/input\\",\\"test/fixtures/dist/extract:path/style.less\\"],\\"names\\":[],\\"mappings\\":\\"AAAA;EACE,WAAW;CACZ;;ACFD;EACE,WAAW;CACZ;;ACFD;EACE,YAAA;EACA,iBAAA;CCCD;AACD,0DAA0D;ACJ1D;EACE,WAAW;EACX,uBAAuB,EAAE;;ACC3B;EACE,eAAA;CCFD\\",\\"file\\":\\"test/fixtures/dist/extract:path/this/is/extracted.css\\",\\"sourcesContent\\":[\\"body {\\\\n  color: red;\\\\n}\\\\n\\",\\".bar {\\\\n  color: red;\\\\n}\\\\n\\",null,null,\\"#sidebar {\\\\n  width: 30%;\\\\n  background-color: #faa; }\\\\n\\",null,null]}"`;
 
 exports[`extract:path: js code 1`] = `
 "'use strict';