diff --git a/sys/netinet6/nd6.c b/sys/netinet6/nd6.c
index e091deefa7dc..d7a0e6ff6bae 100644
--- a/sys/netinet6/nd6.c
+++ b/sys/netinet6/nd6.c
@@ -1894,6 +1894,7 @@ nd6_output(ifp, origifp, m0, dst, rt0)
 			if (rt->rt_gwroute == 0)
 				goto lookup;
 			if (((rt = rt->rt_gwroute)->rt_flags & RTF_UP) == 0) {
+				RT_LOCK(rt);
 				rtfree(rt); rt = rt0;
 			lookup:
 				rt->rt_gwroute = rtalloc1(rt->rt_gateway, 1, 0UL);