diff --git a/program/js/app.js b/program/js/app.js
index 1b3836804..29a53bb26 100644
--- a/program/js/app.js
+++ b/program/js/app.js
@@ -2261,7 +2261,7 @@ function rcube_webmail()
       if (preview && this.message_list && this.message_list.rows[id] && this.message_list.rows[id].unread && this.env.preview_pane_mark_read > 0) {
         this.preview_read_timer = setTimeout(function() {
           ref.set_unread_message(id, ref.env.mailbox);
-          ref.http_post('mark', {_uid: id, _flag: 'read', _quiet: 1});
+          ref.http_post('mark', {_uid: id, _flag: 'read', _mbox: ref.env.mailbox, _quiet: 1});
         }, this.env.preview_pane_mark_read * 1000);
       }
     }