diff --git a/themes/hugo-sustain/layouts/partials/head.html b/themes/hugo-sustain/layouts/partials/head.html
index ed42ce1..83373ae 100644
--- a/themes/hugo-sustain/layouts/partials/head.html
+++ b/themes/hugo-sustain/layouts/partials/head.html
@@ -24,7 +24,7 @@
     <link rel="stylesheet" type="text/css" href="{{ .Site.BaseURL }}css/fontawesome/css/all.min.css" />
     <link rel="stylesheet" type="text/css" href="{{ .Site.BaseURL }}css/fonts.css" />
     {{ range .Site.Params.custom_css }}
-    <link rel="stylesheet" href="{{ $.Site.BaseURL}}{{ . }}" />
+    <link rel="stylesheet" href="{{ $.Site.BaseURL}}{{ . }}?v={{ md5 $.Hugo.BuildDate }}" />
     {{ end }}
     {{ `<!--[if lt IE 9]>
 			<script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>