diff --git a/package.json b/package.json
index 3b9d368..fd4c189 100644
--- a/package.json
+++ b/package.json
@@ -63,7 +63,7 @@
     "nyc": "^10.1.2",
     "postcss-at-rules-variables": "^0.1.0",
     "postcss-cli": "^3.1.1",
-    "postcss-custom-properties": "^5.0.2",
+    "postcss-custom-properties": "^6.0.0",
     "postcss-discard-comments": "^2.0.4",
     "postcss-each": "^0.9.3",
     "prettier": "^1.3.1",