diff --git a/gr-editor/gr-editor.js b/gr-editor/gr-editor.js
index 322eb10..ad88d9e 100644
--- a/gr-editor/gr-editor.js
+++ b/gr-editor/gr-editor.js
@@ -60,7 +60,7 @@
     _importCodeMirror() {
       const url = this.plugin.url('/static/codemirror-assets.html');
       return new Promise((resolve, reject) => {
-        this.importHref(url, resolve, reject);
+        (this.importHref || Polymer.importHref)(url, resolve, reject);
       });
     },