diff --git a/lib/utils/templatize.js b/lib/utils/templatize.js
index 4e42ae6fe1..60a2a8b104 100644
--- a/lib/utils/templatize.js
+++ b/lib/utils/templatize.js
@@ -392,21 +392,31 @@ function addPropagateEffects(target, templateInfo, options, methodHost) {
          * @constructor
          * @extends {DataTemplate}
          */
-        let templatizedBase = options.mutableData ? MutableDataTemplate : DataTemplate;
+        let templatizedBase =
+            options.mutableData ? MutableDataTemplate : DataTemplate;
+
+        // NOTE: due to https://github.com/google/closure-compiler/issues/2928,
+        // combining the next two lines into one assignment causes a spurious
+        // type error.
+        class TemplatizedTemplate extends templatizedBase {}
         /** @private */
-        klass = templateInfo.templatizeTemplateClass =
-          class TemplatizedTemplate extends templatizedBase {};
+        klass = templateInfo.templatizeTemplateClass = TemplatizedTemplate;
       } else {
         /**
          * @constructor
          * @extends {PolymerElement}
          */
         const templatizedBase = target.constructor;
+
         // Create a cached subclass of the base custom element class onto which
         // to put the template-specific propagate effects
+        // NOTE: due to https://github.com/google/closure-compiler/issues/2928,
+        // combining the next two lines into one assignment causes a spurious
+        // type error.
+        class TemplatizedTemplateExtension extends templatizedBase {}
         /** @private */
         klass = templateInfo.templatizeTemplateClass =
-          class TemplatizedTemplateExtension extends templatizedBase {};
+            TemplatizedTemplateExtension;
       }
       // Add template - >instances effects
       // and host <- template effects