diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 530b947783..6334f26514 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -6385,6 +6385,9 @@ get_shadow_width (GtkWidget *widget,
       priv->tiled)
     return;
 
+  if (!gtk_widget_is_toplevel (widget))
+    return;
+
   state = gtk_widget_get_state_flags (widget);
   context = gtk_widget_get_style_context (widget);