diff --git a/src/wrappers.js b/src/wrappers.js
index 7e89655..f3a2bb3 100644
--- a/src/wrappers.js
+++ b/src/wrappers.js
@@ -30,16 +30,19 @@ window.ShadowDOMPolyfill = {};
       throw new Error('Assertion failed');
   };
 
+  var defineProperty = Object.defineProperty;
+  var getOwnPropertyNames = Object.getOwnPropertyNames;
+  var getOwnPropertyDescriptor = Object.getOwnPropertyDescriptor;
+
   function mixin(to, from) {
-    Object.getOwnPropertyNames(from).forEach(function(name) {
-      Object.defineProperty(to, name,
-                            Object.getOwnPropertyDescriptor(from, name));
+    getOwnPropertyNames(from).forEach(function(name) {
+      defineProperty(to, name, getOwnPropertyDescriptor(from, name));
     });
     return to;
   };
 
   function mixinStatics(to, from) {
-    Object.getOwnPropertyNames(from).forEach(function(name) {
+    getOwnPropertyNames(from).forEach(function(name) {
       switch (name) {
         case 'arguments':
         case 'caller':
@@ -49,8 +52,7 @@ window.ShadowDOMPolyfill = {};
         case 'toString':
           return;
       }
-      Object.defineProperty(to, name,
-                            Object.getOwnPropertyDescriptor(from, name));
+      defineProperty(to, name, getOwnPropertyDescriptor(from, name));
     });
     return to;
   };
@@ -65,7 +67,7 @@ window.ShadowDOMPolyfill = {};
   // Mozilla's old DOM bindings are bretty busted:
   // https://bugzilla.mozilla.org/show_bug.cgi?id=855844
   // Make sure they are create before we start modifying things.
-  Object.getOwnPropertyNames(window);
+  getOwnPropertyNames(window);
 
   function getWrapperConstructor(node) {
     var nativePrototype = node.__proto__ || Object.getPrototypeOf(node);
@@ -128,7 +130,7 @@ window.ShadowDOMPolyfill = {};
   }
 
   function installProperty(source, target, allowMethod) {
-    Object.getOwnPropertyNames(source).forEach(function(name) {
+    getOwnPropertyNames(source).forEach(function(name) {
       if (name in target)
         return;
 
@@ -138,7 +140,7 @@ window.ShadowDOMPolyfill = {};
       }
       var descriptor;
       try {
-        descriptor = Object.getOwnPropertyDescriptor(source, name);
+        descriptor = getOwnPropertyDescriptor(source, name);
       } catch (ex) {
         // JSC and V8 both use data properties instead of accessors which can
         // cause getting the property desciptor to throw an exception.
@@ -164,7 +166,7 @@ window.ShadowDOMPolyfill = {};
           setter = getSetter(name);
       }
 
-      Object.defineProperty(target, name, {
+      defineProperty(target, name, {
         get: getter,
         set: setter,
         configurable: descriptor.configurable,
@@ -195,6 +197,12 @@ window.ShadowDOMPolyfill = {};
     addForwardingProperties(nativePrototype, wrapperPrototype);
     if (opt_instance)
       registerInstanceProperties(wrapperPrototype, opt_instance);
+    defineProperty(wrapperPrototype, 'constructor', {
+      value: wrapperConstructor,
+      configurable: true,
+      enumerable: false,
+      writable: true
+    });
   }
 
   function isWrapperFor(wrapperConstructor, nativeConstructor) {
@@ -205,11 +213,7 @@ window.ShadowDOMPolyfill = {};
   /**
    * Creates a generic wrapper constructor based on |object| and its
    * constructor.
-   * Sometimes the constructor does not have an associated instance
-   * (CharacterData for example). In that case you can pass the constructor that
-   * you want to map the object to using |opt_nativeConstructor|.
    * @param {Node} object
-   * @param {Function=} opt_nativeConstructor
    * @return {Function} The generated constructor.
    */
   function registerObject(object) {
@@ -322,7 +326,7 @@ window.ShadowDOMPolyfill = {};
   }
 
   function defineGetter(constructor, name, getter) {
-    Object.defineProperty(constructor.prototype, name, {
+    defineProperty(constructor.prototype, name, {
       get: getter,
       configurable: true,
       enumerable: true
diff --git a/test/js/wrappers.js b/test/js/wrappers.js
index 5c6957b..519d4dd 100644
--- a/test/js/wrappers.js
+++ b/test/js/wrappers.js
@@ -17,6 +17,13 @@ suite('Wrapper creation', function() {
     assert.isTrue(Object.getPrototypeOf(br).hasOwnProperty('clear'));
   });
 
+  test('HTMLUnknownElement constructor', function() {
+    var element = document.createElement('unknownelement');
+    assert.instanceOf(element, HTMLUnknownElement);
+    assert.equal(Object.getPrototypeOf(element), HTMLUnknownElement.prototype);
+    assert.equal(Object.getPrototypeOf(element).constructor, HTMLUnknownElement);
+  });
+
   Object.keys(knownElements).forEach(function(tagName) {
     test(tagName, function() {
       var constructor = window[knownElements[tagName]];
@@ -26,6 +33,7 @@ suite('Wrapper creation', function() {
       var element = document.createElement(tagName);
       assert.instanceOf(element, constructor);
       assert.equal(Object.getPrototypeOf(element), constructor.prototype);
+      assert.equal(Object.getPrototypeOf(element).constructor, constructor);
     });
   });