diff --git a/program/include/rcube_shared.inc b/program/include/rcube_shared.inc
index 5008251ad..4d35a4d9b 100644
--- a/program/include/rcube_shared.inc
+++ b/program/include/rcube_shared.inc
@@ -504,7 +504,7 @@ function get_offset_time($offset_str, $factor=1)
  * @see    http://de2.php.net/manual/en/ref.fileinfo.php
  * @see    http://de2.php.net/mime_content_type
  */
-function rc_mime_content_type($path, $failover = 'unknown/unknown')
+function rc_mime_content_type($path, $failover = 'application/octet-stream')
 {
     $mime_type = null;
     $mime_magic = rcmail::get_instance()->config->get('mime_magic');