diff --git a/lib/minimizer/css.php b/lib/minimizer/css.php
index f8e84482bb..110935ea3b 100644
--- a/lib/minimizer/css.php
+++ b/lib/minimizer/css.php
@@ -17,7 +17,7 @@ class OC_Minimizer_CSS extends OC_Minimizer
 			$in_root = false;
 			foreach(OC::$APPSROOTS as $app_root) {
 				if(strpos($file, $app_root['path']) === 0) {
-					$in_root = $webroot.$app_root['url'];
+					$in_root = rtrim($webroot.$app_root['url'], '/');
 					break;
 				}
 			}