diff --git a/xmenu.c b/xmenu.c
index afb4301..a4c29e1 100644
--- a/xmenu.c
+++ b/xmenu.c
@@ -432,6 +432,10 @@ buildmenutree(unsigned level, const char *label, const char *output, char *file)
 		for (item = prevmenu->list; item->next != NULL; item = item->next)
 			;
 
+		/* a separator is no valid root for a submenu */
+		if (!item->label)
+			errx(1, "a separator is no valid root for a submenu");
+
 		prevmenu = menu;
 		menu->caller = item;
 		item->submenu = menu;