diff --git a/package.json b/package.json
index ffd9b74091..8d6e10c67e 100644
--- a/package.json
+++ b/package.json
@@ -50,7 +50,7 @@
     "walk": "2.3.9"
   },
   "devDependencies": {
-    "clean-css": "3.4.20",
+    "clean-css": "3.4.21",
     "coveralls": "2.11.15",
     "debounce": "^1.0.0",
     "eslint": "3.10.2",