diff --git a/packages/custom-elements/src/CustomElementRegistry.js b/packages/custom-elements/src/CustomElementRegistry.js
index 1752da79b..0e7b035f2 100644
--- a/packages/custom-elements/src/CustomElementRegistry.js
+++ b/packages/custom-elements/src/CustomElementRegistry.js
@@ -168,9 +168,6 @@ export default class CustomElementRegistry {
     try {
       /** @type {!Object} */
       const prototype = constructor.prototype;
-      if (!(prototype instanceof Object)) {
-        throw new TypeError('The custom element constructor\'s prototype is not an object.');
-      }
 
       function getCallback(name) {
         const callbackValue = prototype[name];