diff --git a/includes/common.inc b/includes/common.inc
index 0a3ed73..cee3f31 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -3456,6 +3456,7 @@ function _drupal_build_css_path($matches, $base = NULL) {
     $last = $path;
     $path = preg_replace('`(^|/)(?!\.\./)([^/]+)/\.\./`', '$1', $path);
   }
+  $path .= (strpos($path, '?') === FALSE ? '?version=' : '&version=') . variable_get('drupal_css_cache_version', 1);
   return 'url(' . $path . ')';
 }