diff --git a/build.sbt b/build.sbt
index 50f99b1..a02a1da 100755
--- a/build.sbt
+++ b/build.sbt
@@ -20,7 +20,7 @@ libraryDependencies ++= Seq(
   "org.webjars.npm" % "less" % "4.2.0",
   "org.webjars.npm" % "clone" % "2.1.2",
   "org.webjars.npm" % "mkdirp" % "0.5.6",
-  "org.webjars.npm" % "clean-css" % "4.2.4",
+  "org.webjars.npm" % "clean-css" % "5.3.2",
   "org.webjars.npm" % "less-plugin-clean-css" % "1.5.1" intransitive(),
   "org.webjars.npm" % "es6-promise" % "4.2.8"
 )