diff --git a/plugins/kolab_addressbook/kolab_addressbook.js b/plugins/kolab_addressbook/kolab_addressbook.js
index 941c7200..e2f700a1 100644
--- a/plugins/kolab_addressbook/kolab_addressbook.js
+++ b/plugins/kolab_addressbook/kolab_addressbook.js
@@ -164,7 +164,7 @@ rcube_webmail.prototype.book_delete = function()
     if (this.env.source != '') {
         this.confirm_dialog(this.get_label('kolab_addressbook.bookdeleteconfirm'), 'delete', function() {
             var lock = rcmail.set_busy(true, 'kolab_addressbook.bookdeleting');
-            rcmail.http_request('plugin.book', '_act=delete&_source='+urlencode(this.book_realname()), lock);
+            rcmail.http_request('plugin.book', '_act=delete&_source='+urlencode(rcmail.book_realname()), lock);
         });
     }
 };