diff --git a/program/js/app.js b/program/js/app.js
index ff7411c13..069c59fbd 100644
--- a/program/js/app.js
+++ b/program/js/app.js
@@ -1824,6 +1824,8 @@ function rcube_webmail()
     else {
       if (!this.env.frame_lock)
         this.env.frame_lock = this.set_busy(true, 'loading');
+      if (preview)
+        url += '&_unlock='+this.env.frame_lock;
       target.location.href = this.env.comm_path+url;
 
       // mark as read and change mbox unread counter