diff --git a/lib/private/Template/SCSSCacher.php b/lib/private/Template/SCSSCacher.php
index 09c7f604273..0b85af3f27f 100644
--- a/lib/private/Template/SCSSCacher.php
+++ b/lib/private/Template/SCSSCacher.php
@@ -282,7 +282,7 @@ class SCSSCacher {
 	 */
 	private function rebaseUrls($css, $webDir) {
 		$re = '/url\([\'"]([\.\w?=\/-]*)[\'"]\)/x';
-		$subst = 'url('.$webDir.'/$1)';
+		$subst = 'url(\''.$webDir.'/$1\')';
 		return preg_replace($re, $subst, $css);
 	}