diff --git a/sys/netinet6/nd6_rtr.c b/sys/netinet6/nd6_rtr.c
--- a/sys/netinet6/nd6_rtr.c
+++ b/sys/netinet6/nd6_rtr.c
@@ -269,6 +269,7 @@
 	dr0.advint_expire = 0;	/* Mobile IPv6 */
 	dr0.advints_lost = 0;	/* Mobile IPv6 */
 	/* unspecified or not? (RFC 2461 6.3.4) */
+	/* XXX: ndi fields modified without nd6_mtx (DF-0419) */
 	if (advreachable) {
 		advreachable = ntohl(advreachable);
 		if (advreachable <= MAX_REACHABLE_TIME &&