diff --git a/mozilla/docshell/base/nsDocShell.cpp b/mozilla/docshell/base/nsDocShell.cpp
index 12b8a8d79c3..d63267a7185 100644
--- a/mozilla/docshell/base/nsDocShell.cpp
+++ b/mozilla/docshell/base/nsDocShell.cpp
@@ -2855,6 +2855,10 @@ NS_IMETHODIMP nsDocShell::SetupNewViewer(nsIContentViewer* aNewViewer)
 
    nsCOMPtr<nsIWidget> widget;
    NS_ENSURE_SUCCESS(GetMainWidget(getter_AddRefs(widget)), NS_ERROR_FAILURE);
+   if (!widget) {
+     NS_ERROR("GetMainWidget coughed up a null widget");
+     return NS_ERROR_FAILURE;
+   }
 
    nsRect bounds(x, y, cx, cy);
    NS_ENSURE_SUCCESS(EnsureDeviceContext(), NS_ERROR_FAILURE);