diff --git a/test/js/customElements.js b/test/js/customElements.js
index 5d5c41f..f48b9b0 100644
--- a/test/js/customElements.js
+++ b/test/js/customElements.js
@@ -36,6 +36,16 @@ suite('customElements', function() {
     assert.ok(false, 'document.registerElement failed to throw when given no arguments');
   });
 
+  // http://w3c.github.io/webcomponents/spec/custom/#extensions-to-document-interface-to-register
+  test('document.registerElement second argument is optional', function() {
+    try {
+      document.registerElement('x-no-proto');
+    } catch(x) {
+      return;
+    }
+    assert.ok(true, 'document.registerElement failed to function without ElementRegistionOptions argument');
+  });
+
   test('document.registerElement requires name argument to not conflict with a reserved name', function() {
     try {
       document.registerElement('font-face', {prototype: Object.create(HTMLElement.prototype)});