diff --git a/extensions/css-language-features/server/src/requests.ts b/extensions/css-language-features/server/src/requests.ts
index 6e708421d2b..79f166c2d40 100644
--- a/extensions/css-language-features/server/src/requests.ts
+++ b/extensions/css-language-features/server/src/requests.ts
@@ -113,9 +113,26 @@ export function basename(uri: string) {
 	return uri.substr(lastIndexOfSlash + 1);
 }
 
+
 const Slash = '/'.charCodeAt(0);
 const Dot = '.'.charCodeAt(0);
 
+export function extname(uri: string) {
+	for (let i = uri.length - 1; i >= 0; i--) {
+		const ch = uri.charCodeAt(i);
+		if (ch === Dot) {
+			if (i > 0 && uri.charCodeAt(i - 1) !== Slash) {
+				return uri.substr(i);
+			} else {
+				break;
+			}
+		} else if (ch === Slash) {
+			break;
+		}
+	}
+	return '';
+}
+
 export function isAbsolutePath(path: string) {
 	return path.charCodeAt(0) === Slash;
 }
diff --git a/extensions/css-language-features/server/src/test/requests.test.ts b/extensions/css-language-features/server/src/test/requests.test.ts
index bbec8842ea9..3f287fefed0 100644
--- a/extensions/css-language-features/server/src/test/requests.test.ts
+++ b/extensions/css-language-features/server/src/test/requests.test.ts
@@ -4,8 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 import 'mocha';
 import * as assert from 'assert';
-import { joinPath, normalizePath, resolvePath } from '../requests';
-
+import { joinPath, normalizePath, resolvePath, extname } from '../requests';
 
 suite('requests', () => {
 	test('join', async function () {
@@ -51,4 +50,13 @@ suite('requests', () => {
 		assertNormalize('..', '');
 		assertNormalize('/..', '/');
 	});
+
+	test('extname', async function () {
+		function assertExtName(input: string, expected: string) {
+			assert.equal(extname(input), expected, input);
+		}
+		assertExtName('foo://a/foo/bar', '');
+		assertExtName('foo://a/foo/bar.foo', '.foo');
+		assertExtName('foo://a/foo/.foo', '');
+	});
 });