diff --git a/lib/mixins/mutable-data.html b/lib/mixins/mutable-data.html
index 2cfe3d54d3..0adce76b25 100644
--- a/lib/mixins/mutable-data.html
+++ b/lib/mixins/mutable-data.html
@@ -8,6 +8,8 @@
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 
+<link rel="import" href="../utils/mixin.html">
+
 <script>
 (function() {
   'use strict';
@@ -68,7 +70,7 @@
    * @summary Element class mixin to skip strict dirty-checking for objects
    *   and arrays
    */
-  Polymer.MutableData = (superClass) => {
+  Polymer.MutableData = Polymer.dedupingMixin((superClass) => {
 
     return class MutableData extends superClass {
       /**
@@ -94,7 +96,7 @@
 
     }
 
-  };
+  });
 
   /**
    * Element class mixin to add the optional ability to skip strict
@@ -133,7 +135,7 @@
    * @summary Element class mixin to optionally skip strict dirty-checking
    *   for objects and arrays
    */
-  Polymer.OptionalMutableData = (superClass) => {
+  Polymer.OptionalMutableData = Polymer.dedupingMixin((superClass) => {
 
     return class OptionalMutableData extends superClass {
 
@@ -171,7 +173,7 @@
       }
     }
 
-  };
+  });
 
   // Export for use by legacy behavior
   Polymer.MutableData._mutablePropertyChange = mutablePropertyChange;
diff --git a/lib/utils/templatize.html b/lib/utils/templatize.html
index 82bb74e1c0..5152176ee3 100644
--- a/lib/utils/templatize.html
+++ b/lib/utils/templatize.html
@@ -432,12 +432,13 @@
        *
        * @memberof Polymer.Templatize
        * @method modelForElement
-       * @param {HTMLElement} host
+       * @param {HTMLTemplateElement} template The model will be returned for
+       *   elements stamped from this template
        * @param {HTMLElement} el Element for which to return a template model.
        * @return {TemplateInstanceBase} Template instance representing the
        *   binding scope for the element
        */
-      modelForElement(host, el) {
+      modelForElement(template, el) {
         let model;
         while (el) {
           // An element with a __templatizeInstance marks the top boundary
@@ -446,7 +447,7 @@
           if ((model = el.__templatizeInstance)) {
             // Found an element stamped by another template; keep walking up
             // from its __dataHost
-            if (model.__dataHost != host) {
+            if (model.__dataHost != template) {
               el = model.__dataHost;
             } else {
               return model;