diff --git a/package.json b/package.json
index 8358c99f..df60d445 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,7 @@
     "node": ">= 8.6.0"
   },
   "dependencies": {
-    "clean-css": "4.2.1",
+    "clean-css": "4.2.3",
     "express": "4.17.1",
     "express-history-api-fallback": "2.2.1",
     "highland": "2.13.4",
diff --git a/yarn.lock b/yarn.lock
index 5342afe6..bc1695cd 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -736,7 +736,13 @@ class-utils@^0.3.5:
     isobject "^3.0.0"
     static-extend "^0.1.1"
 
-clean-css@4.2.1, clean-css@^4.2.1:
+clean-css@4.2.3:
+  version "4.2.3"
+  resolved "https://registry.yarnpkg.com/clean-css/-/clean-css-4.2.3.tgz#507b5de7d97b48ee53d84adb0160ff6216380f78"
+  dependencies:
+    source-map "~0.6.0"
+
+clean-css@^4.2.1:
   version "4.2.1"
   resolved "https://registry.yarnpkg.com/clean-css/-/clean-css-4.2.1.tgz#2d411ef76b8569b6d0c84068dabe85b0aa5e5c17"
   dependencies: