diff --git a/iron-list.html b/iron-list.html
index 64f17016..3a26afd2 100644
--- a/iron-list.html
+++ b/iron-list.html
@@ -969,7 +969,7 @@
       var g = window;
       var handle = g.requestIdleCallback ? g.requestIdleCallback(cb) : g.setTimeout(cb, 16);
       // Polymer/issues/3895
-      Polymer.dom.addDebouncer({
+      Polymer.dom.addDebouncer(/** @type {!Polymer.Debouncer} */{
         complete: function() {
           g.cancelIdleCallback ? g.cancelIdleCallback(handle) : g.clearTimeout(handle);
           cb();