diff --git a/inc/inc.Utils.php b/inc/inc.Utils.php
index e26137cb4..f7d7f5026 100644
--- a/inc/inc.Utils.php
+++ b/inc/inc.Utils.php
@@ -380,7 +380,7 @@ function utf8_basename($path, $suffix='') { /* {{{ */
  * @return string valid file name
  */
 function getFilenameByDocname($content) { /* {{{ */
-	if(is_string) {
+	if(is_string($content)) {
 		$filename = $content;
 	} else {
 		$document = $content->getDocument();