diff --git a/externs/polymer-externs.js b/externs/polymer-externs.js
index 7c0ede16aa..0a4aa90272 100644
--- a/externs/polymer-externs.js
+++ b/externs/polymer-externs.js
@@ -122,6 +122,8 @@ PolymerElement.prototype.created = function() {};
  * @override
  */
 PolymerElement.prototype.ready = function() {};
+/** On before register callback. */
+PolymerElement.prototype.beforeRegister = function() {};
 /** On registered callback. */
 PolymerElement.prototype.registered = function() {};
 /**