diff --git a/includes/common.inc b/includes/common.inc
index 9911ef6..22262c6 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -3192,7 +3192,7 @@ function _drupal_build_css_path($matches, $base = NULL) {
     $last = $path;
     $path = preg_replace('`(^|/)(?!\.\./)([^/]+)/\.\./`', '$1', $path);
   }
-  return 'url(' . $path . ')';
+  return 'url("' . $path . '")';
 }
 
 /**