diff --git a/src/dygraphs/package.json b/src/dygraphs/package.json
index bd3603d..203cd1e 100644
--- a/src/dygraphs/package.json
+++ b/src/dygraphs/package.json
@@ -40,7 +40,7 @@
     "browserify": "^11.2.0",
     "browserify-header": "^0.9.2",
     "chai": "^3.3.0",
-    "clean-css": "^3.4.23",
+    "clean-css": "^4.2.1",
     "core-js": "^2.4.1",
     "coveralls": "^2.11.2",
     "envify": "^3.4.0",