diff --git a/lib/legacy/class.html b/lib/legacy/class.html
index 0f10bcbe2a..33f313a1af 100644
--- a/lib/legacy/class.html
+++ b/lib/legacy/class.html
@@ -47,18 +47,21 @@
 
     function copyProperties(source, target, excludeProps) {
       const noAccessors = source._noAccessors;
-      for (let p in source) {
-        if (!(p in excludeProps)) {
-          if (noAccessors) {
-            target[p] = source[p];
-          } else {
-            let pd = Object.getOwnPropertyDescriptor(source, p);
-            if (pd) {
-              // ensure property is configurable so that a later behavior can
-              // re-configure it.
-              pd.configurable = true;
-              Object.defineProperty(target, p, pd);
-            }
+      const propertyNames = Object.getOwnPropertyNames(source);
+      for (let i = 0; i < propertyNames.length; i++) {
+        let p = propertyNames[i];
+        if (p in excludeProps) {
+          continue;
+        }
+        if (noAccessors) {
+          target[p] = source[p];
+        } else {
+          let pd = Object.getOwnPropertyDescriptor(source, p);
+          if (pd) {
+            // ensure property is configurable so that a later behavior can
+            // re-configure it.
+            pd.configurable = true;
+            Object.defineProperty(target, p, pd);
           }
         }
       }
diff --git a/test/runner.html b/test/runner.html
index 2402bb3174..dc0eb5c31b 100644
--- a/test/runner.html
+++ b/test/runner.html
@@ -82,8 +82,9 @@
       'unit/disable-upgrade.html',
       'unit/shady-unscoped-style.html',
       'unit/html-tag.html',
-      'unit/legacy-data.html'
+      'unit/legacy-data.html',
       // 'unit/multi-style.html'
+      'unit/class-properties.html'
     ];
 
     function combinations(suites, flags) {
diff --git a/test/unit/class-properties.html b/test/unit/class-properties.html
new file mode 100644
index 0000000000..8924e93572
--- /dev/null
+++ b/test/unit/class-properties.html
@@ -0,0 +1,38 @@
+<!doctype html>
+<!--
+@license
+Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<html>
+<head>
+  <meta charset="utf-8">
+  <script src="../../../webcomponentsjs/webcomponents-lite.js"></script>
+  <script src="../../../web-component-tester/browser.js"></script>
+  <link rel="import" href="../../polymer.html">
+</head>
+<body>
+  <script>
+    class Example {
+      ready() {}
+      foo() {}
+    }
+    Example.prototype.is = 'x-example';
+
+    suite('Polymer function w/Class', function() {
+      test('Polymer call works with a class', function() {
+        assert.doesNotThrow(() => Polymer(Example.prototype));
+      });
+      test('methods are copied from class input', function() {
+        const def = customElements.get('x-example');
+        assert(def.prototype.ready, 'ready should be defined');
+        assert(def.prototype.foo, 'foo should be defined');
+      });
+    });
+  </script>
+</body>
+</html>
\ No newline at end of file
