diff --git a/plugins/kolab_files/lib/kolab_files_engine.php b/plugins/kolab_files/lib/kolab_files_engine.php
index 1f15ae7e..cae47016 100644
--- a/plugins/kolab_files/lib/kolab_files_engine.php
+++ b/plugins/kolab_files/lib/kolab_files_engine.php
@@ -1280,7 +1280,7 @@ class kolab_files_engine
                     'html'      => $content,
                     'name'      => $attachment['name'],
                     'mimetype'  => $attachment['mimetype'],
-                    'classname' => rcmail_filetype2classname($attachment['mimetype'], $attachment['name']),
+                    'classname' => rcube_utils::file2class($attachment['mimetype'], $attachment['name']),
                     'complete'  => true), $uploadid);
             }
             else if ($attachment['error']) {