--- src/sys/net/if.c	2004/09/10 14:02:00	1.20
+++ src/sys/net/if.c	2004/09/13 23:45:57	1.21
@@ -320,6 +320,8 @@ if_detach(ifp)
 	/* Announce that the interface is gone. */
 	rt_ifannouncemsg(ifp, IFAN_DEPARTURE);
 
+	ifindex2ifnet[ifp->if_index] = NULL;
+
 	TAILQ_REMOVE(&ifnet, ifp, if_link);
 	splx(s);
 }