diff --git a/lib/mixins/disable-upgrade-mixin.html b/lib/mixins/disable-upgrade-mixin.html
index 1df07f6666..17af982799 100644
--- a/lib/mixins/disable-upgrade-mixin.html
+++ b/lib/mixins/disable-upgrade-mixin.html
@@ -9,6 +9,7 @@
 -->
 <script>
 (function() {
+  'use strict';
 
   const DISABLED_ATTR = 'disable-upgrade';
 
@@ -79,7 +80,8 @@
         }
       }
 
-    }
+    };
+
   });
 
 })();
diff --git a/test/unit/disable-upgrade.html b/test/unit/disable-upgrade.html
index 409b63237e..fd2b6cb1f7 100644
--- a/test/unit/disable-upgrade.html
+++ b/test/unit/disable-upgrade.html
@@ -39,7 +39,7 @@ <h2 id="element">[[prop]]</h2>
             prop: {
               type: String
             }
-          }
+          };
         }
         constructor() {
           super();
@@ -71,7 +71,7 @@ <h2 id="element">[[prop]]</h2>
         static get properties() {
           return {
             upgradeDisabled: {value: true}
-          }
+          };
         }
         enable() {
           this.$.disabledEl.removeAttribute('disable-upgrade');