diff --git a/externs/closure-types.js b/externs/closure-types.js
index 7d03a31482..b72307604c 100644
--- a/externs/closure-types.js
+++ b/externs/closure-types.js
@@ -756,9 +756,8 @@ Polymer_ElementMixin.finalize = function(){};
 Polymer_ElementMixin._processStyleText = function(cssText, baseURI){};
 /**
 * @param {string} is Tag name (or type extension name) for this element
-* @param {string=} ext For type extensions, the tag name that was extended
 */
-Polymer_ElementMixin._finalizeTemplate = function(is, ext){};
+Polymer_ElementMixin._finalizeTemplate = function(is){};
 /**
 * @interface
 */
diff --git a/lib/mixins/element-mixin.html b/lib/mixins/element-mixin.html
index 842aacad21..9aee47d642 100644
--- a/lib/mixins/element-mixin.html
+++ b/lib/mixins/element-mixin.html
@@ -406,11 +406,10 @@
      * @param {PolymerElementConstructor} klass Element class
      * @param {!HTMLTemplateElement} template Template to process
      * @param {string} is Name of element
-     * @param {string} ext Name of native element
      * @param {string} baseURI Base URI for element
      * @private
      */
-    function processElementStyles(klass, template, is, ext, baseURI) {
+    function processElementStyles(klass, template, is, baseURI) {
       const styles = Polymer.StyleGather.stylesFromModuleImports(is).concat(
         Polymer.StyleGather.stylesFromTemplate(template));
       let templateStyles = template.content.querySelectorAll('style');
@@ -426,7 +425,7 @@
         s.textContent = klass._processStyleText(s.textContent, baseURI);
       }
       if (window.ShadyCSS) {
-        window.ShadyCSS.prepareTemplate(template, is, ext);
+        window.ShadyCSS.prepareTemplate(template, is);
       }
     }
 
@@ -626,10 +625,9 @@
       * style scoping.
       *
       * @param {string} is Tag name (or type extension name) for this element
-      * @param {string=} ext For type extensions, the tag name that was extended
       * @protected
       */
-      static _finalizeTemplate(is, ext) {
+      static _finalizeTemplate(is) {
         /** @const {HTMLTemplateElement} */
         const template = this.prototype._template;
         if (template && !template.__polymerFinalized) {
@@ -637,7 +635,7 @@
           const importPath = this.importPath;
           const baseURI = importPath ? Polymer.ResolveUrl.resolveUrl(importPath) : '';
           // e.g. support `include="module-name"`, and ShadyCSS
-          processElementStyles(this, template, is, ext, baseURI);
+          processElementStyles(this, template, is, baseURI);
           this.prototype._bindTemplate(template);
         }
       }