diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index 683e0e52e06..9a150d6cf9d 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -573,29 +573,33 @@ nsDocumentViewer::SyncParentSubDocMap()
   }
 
   nsCOMPtr<nsPIDOMWindow> pwin(docShell->GetWindow());
-  nsCOMPtr<Element> element;
-  if (mDocument && pwin) {
-    element = pwin->GetFrameElementInternal();
+  if (!mDocument || !pwin) {
+    return NS_OK;
   }
 
-  if (element) {
-    nsCOMPtr<nsIDocShellTreeItem> parent;
-    docShell->GetParent(getter_AddRefs(parent));
-
-    nsCOMPtr<nsPIDOMWindow> parent_win = parent ? parent->GetWindow() : nullptr;
-    if (parent_win) {
-      nsCOMPtr<nsIDocument> parent_doc = parent_win->GetDoc();
-      if (parent_doc) {
-        if (mDocument && parent_doc->GetSubDocumentFor(element) != mDocument) {
-          mDocument->SuppressEventHandling(nsIDocument::eEvents,
-                                           parent_doc->EventHandlingSuppressed());
-        }
-        return parent_doc->SetSubDocumentFor(element, mDocument);
-      }
-    }
+  nsCOMPtr<Element> element = pwin->GetFrameElementInternal();
+  if (!element) {
+    return NS_OK;
   }
 
-  return NS_OK;
+  nsCOMPtr<nsIDocShellTreeItem> parent;
+  docShell->GetParent(getter_AddRefs(parent));
+
+  nsCOMPtr<nsPIDOMWindow> parent_win = parent ? parent->GetWindow() : nullptr;
+  if (!parent_win) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIDocument> parent_doc = parent_win->GetDoc();
+  if (!parent_doc) {
+    return NS_OK;
+  }
+
+  if (mDocument && parent_doc->GetSubDocumentFor(element) != mDocument) {
+    mDocument->SuppressEventHandling(nsIDocument::eEvents,
+                                     parent_doc->EventHandlingSuppressed());
+  }
+  return parent_doc->SetSubDocumentFor(element, mDocument);
 }
 
 NS_IMETHODIMP