diff --git a/lib/browser/register-element.ts b/lib/browser/register-element.ts
index f590f0c60..23fd30d4e 100644
--- a/lib/browser/register-element.ts
+++ b/lib/browser/register-element.ts
@@ -26,7 +26,7 @@ function patchCallbacks(target: any, targetName: string, method: string, callbac
           if (descriptor && descriptor.value) {
             descriptor.value = wrapWithCurrentZone(descriptor.value, source);
             _redefineProperty(opts.prototype, callback, descriptor);
-          } else {
+          } else if (prototype[callback]) {
             prototype[callback] = wrapWithCurrentZone(prototype[callback], source);
           }
         } else if (prototype[callback]) {