diff --git a/plugins/kolab_files/lib/kolab_files_engine.php b/plugins/kolab_files/lib/kolab_files_engine.php
index 3fcd270f..cf920f12 100644
--- a/plugins/kolab_files/lib/kolab_files_engine.php
+++ b/plugins/kolab_files/lib/kolab_files_engine.php
@@ -774,7 +774,7 @@ class kolab_files_engine
 
         // editor requires additional arguments via POST
         if (!empty($this->file_data['viewer']['post'])) {
-            $attrib['src'] = $this->rc->output->asset_url('program/resources/blank.gif');
+            $attrib['src'] = 'program/resources/blank.gif';
 
             $form_content = new html_hiddenfield();
             $form_attrib  = array(