diff --git a/source/impressum.html.slim b/source/impressum.html.slim
index 39cafea..066ead2 100644
--- a/source/impressum.html.slim
+++ b/source/impressum.html.slim
@@ -205,7 +205,7 @@
   p
    strong Piwik
   /! piwik
-  iframe frameborder="no" height="250px" src="http://piwik.higgsboson.tk/index.php?module=CoreAdminHome&action=optOut&language=de" width="600px"
+  iframe frameborder="no" height="250px" src="//piwik.higgsboson.tk/index.php?module=CoreAdminHome&action=optOut&language=de" width="600px"
   /! piwik
   p
     strong Quellen: