diff --git a/lib/utils/style-gather.html b/lib/utils/style-gather.html
index d4a141e981..3b0a48da6a 100644
--- a/lib/utils/style-gather.html
+++ b/lib/utils/style-gather.html
@@ -123,7 +123,9 @@
           // other dom-modules that contain styling
           let include = e.getAttribute(INCLUDE_ATTR);
           if (include) {
-            styles.push(...new Set(this.stylesFromModules(include)));
+            styles.push(...this.stylesFromModules(include).filter(function(item, index, self) {
+              return self.indexOf(item) === index;
+            }));
           }
           if (baseURI) {
             e.textContent = Polymer.ResolveUrl.resolveCss(e.textContent, baseURI);