diff --git a/library/attach_mod/includes/functions_attach.php b/library/attach_mod/includes/functions_attach.php
index 3080710c7..c4e86d0cb 100644
--- a/library/attach_mod/includes/functions_attach.php
+++ b/library/attach_mod/includes/functions_attach.php
@@ -410,7 +410,7 @@ function attachment_sync_topic($topics)
  */
 function get_extension($filename)
 {
-    if (false === strstr($filename, '.')) {
+    if (false === strpos($filename, '.')) {
         return '';
     }
     $extension = strrchr(strtolower($filename), '.');