diff --git a/plugins/kolab_files/lib/kolab_files_engine.php b/plugins/kolab_files/lib/kolab_files_engine.php
index fc14e807..67905b02 100644
--- a/plugins/kolab_files/lib/kolab_files_engine.php
+++ b/plugins/kolab_files/lib/kolab_files_engine.php
@@ -610,6 +610,9 @@ class kolab_files_engine
             $this->request->setUrl($url);
         }
 
+        // some HTTP server configurations require this header
+        $this->request->setHeader('accept', "application/json,text/javascript,*/*");
+
         return $this->request;
     }