diff --git a/widget/src/xpwidgets/nsBaseWidget.cpp b/widget/src/xpwidgets/nsBaseWidget.cpp
index 704be15d6680..a2f28d5b5292 100644
--- a/widget/src/xpwidgets/nsBaseWidget.cpp
+++ b/widget/src/xpwidgets/nsBaseWidget.cpp
@@ -312,6 +312,7 @@ NS_IMETHODIMP nsBaseWidget::SetZIndex(PRInt32 aZIndex)
 					if (NS_SUCCEEDED(childWidget->GetZIndex(&childZIndex))) {
 						if (aZIndex < childZIndex) {
 							parent->mChildren->InsertElementAt(this, index);
+							PlaceBehind(childWidget, PR_FALSE);
 							break;
 						}
 					}