--- a/mobile/android/chrome/geckoview/GeckoViewContent.js
+++ b/mobile/android/chrome/geckoview/GeckoViewContent.js
@@ -67,16 +67,17 @@ class GeckoViewContent extends GeckoView
   collectSessionState() {
     let history = SessionHistory.collect(docShell);
     let [formdata, scrolldata] = Utils.mapFrameTree(content, FormData.collect, ScrollPosition.collect);
 
     // Save the current document resolution.
     let zoom = { value: 1 };
     let domWindowUtils = content.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
     domWindowUtils.getResolution(zoom);
+    scrolldata = scrolldata || {};
     scrolldata.zoom = {};
     scrolldata.zoom.resolution = zoom.value;
 
     // Save some data that'll help in adjusting the zoom level
     // when restoring in a different screen orientation.
     let displaySize = {};
     let width = {}, height = {};
     domWindowUtils.getContentViewerSize(width, height);