diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index aaf765102d6..84f21664fac 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -2279,7 +2279,9 @@ DocumentViewerImpl::MakeWindow(const nsSize& aSize, nsIView* aContainerView)
     nsWindowType winType;
     containerItem->GetItemType(&docType);
     mParentWidget->GetWindowType(winType);
-    if (winType == eWindowType_toplevel &&
+    if ((winType == eWindowType_toplevel ||
+         winType == eWindowType_dialog ||
+         winType == eWindowType_invisible) &&
         docType == nsIDocShellTreeItem::typeChrome) {
       // If the old view is already attached to our parent, detach
       DetachFromTopLevelWidget();
diff --git a/widget/src/xpwidgets/nsBaseWidget.cpp b/widget/src/xpwidgets/nsBaseWidget.cpp
index 0975b9cf537..1a42bac6b69 100644
--- a/widget/src/xpwidgets/nsBaseWidget.cpp
+++ b/widget/src/xpwidgets/nsBaseWidget.cpp
@@ -292,7 +292,10 @@ NS_IMETHODIMP
 nsBaseWidget::AttachViewToTopLevel(EVENT_CALLBACK aViewEventFunction,
                                    nsIDeviceContext *aContext)
 {
-  NS_ASSERTION((mWindowType == eWindowType_toplevel), "Can't attach to child?");
+  NS_ASSERTION((mWindowType == eWindowType_toplevel ||
+                mWindowType == eWindowType_dialog ||
+                mWindowType == eWindowType_invisible),
+               "Can't attach to child?");
 
   mViewCallback = aViewEventFunction;