diff --git a/src/lib/base.html b/src/lib/base.html
index 1223d4e438..7d24ebf4ab 100644
--- a/src/lib/base.html
+++ b/src/lib/base.html
@@ -68,6 +68,11 @@
         }
         // registration extension point
         proto._doBehavior('registered');
+        // where prototypes are simulated (IE10), element instance
+        // must be specfically fixed up.
+        if (settings.usePolyfillProto && proto !== this) {
+          proto.extend(this, proto);
+        }
       }
     },
 
diff --git a/test/unit/lazy-register.html b/test/unit/lazy-register.html
index aa64431c0e..88cae90dda 100644
--- a/test/unit/lazy-register.html
+++ b/test/unit/lazy-register.html
@@ -35,6 +35,51 @@
   });
   </script>
 
+  <dom-module id="x-lazy-api">
+    <template>
+      <style>
+        :host {
+          background: red;
+        }
+      </style>
+      <div id="lazy">{{a}}</div>
+    </template>
+    <script>
+    HTMLImports.whenReady(function() {
+      Polymer({
+        is: 'x-lazy-api',
+        go: sinon.spy()
+      });
+    });
+    </script>
+  </dom-module>
+
+  <dom-module id="x-lazy-binding">
+    <template>
+      <style>
+        :host {
+          background: red;
+        }
+      </style>
+      <div id="lazy">{{a}}</div>
+    </template>
+    <script>
+    HTMLImports.whenReady(function() {
+      Polymer({
+        is: 'x-lazy-binding',
+        properties: {
+          a: {
+            value: 'a',
+            observer: '_aChanged'
+          }
+        },
+
+        _aChanged: sinon.spy()
+      });
+    });
+    </script>
+  </dom-module>
+
   <dom-module id="x-lazy-style">
     <template>
       <style>
@@ -78,7 +123,8 @@
   test('not registered until first instance', function() {
     assert.isFalse(window.XLazy.prototype.registered.called, 'registered called before instance created');
     document.createElement('x-lazy');
-    assert.isTrue(window.XLazy.prototype.registered.called, 'registered not called after instance created');
+    document.createElement('x-lazy');
+    assert.isTrue(window.XLazy.prototype.registered.calledOnce, 'registered not called after instance created');
   });
 
   test('registered when `ensureRegisterFinished()` is called', function() {
@@ -88,6 +134,19 @@
     assert.isTrue(window.XLazy.prototype.registered.calledOnce, 'registered called more than once');
   });
 
+  test('bindings and oservers can register lazily', function() {
+    var e = document.createElement('x-lazy-binding');
+    assert.equal(e.$.lazy.textContent, 'a');
+    assert.isTrue(e._aChanged.calledOnce);  
+  });
+
+  test('api can register lazily', function() {
+    var e = document.createElement('x-lazy-api');
+    assert.ok(e.go);
+    e.go();
+    assert.isTrue(e.go.calledOnce);  
+  });
+
   test('styles shimmed at first instance', function() {
     assert.notOk(document.querySelector('style[scope=x-lazy-style]'), 'style shimmed before registration complete');
     document.createElement('x-lazy-style');