diff --git a/misc/ajax.js b/misc/ajax.js
index 63dd65f..e829be8 100644
--- a/misc/ajax.js
+++ b/misc/ajax.js
@@ -622,7 +622,7 @@ Drupal.ajax.prototype.commands = {
    * Command to update a form's build ID.
    */
   updateBuildId: function(ajax, response, status) {
-    $('input[name="form_build_id"][value="' + response.old + '"]').val(response.new);
+    $('input[name="form_build_id"][value="' + response.old + '"]').val(response["new"]);
   }
 };