diff --git a/sys/netinet6/nd6.c b/sys/netinet6/nd6.c
index ef9e37480c9..0a162eb6a55 100644
--- a/sys/netinet6/nd6.c
+++ b/sys/netinet6/nd6.c
@@ -1227,7 +1227,7 @@ nd6_is_new_addr_neighbor(const struct sockaddr_in6 *addr, struct ifnet *ifp)
 	struct ifaddr *dstaddr;
 	struct rt_addrinfo info;
 	struct sockaddr_in6 rt_key;
-	struct sockaddr *dst6;
+	const struct sockaddr *dst6;
 	int fibnum;
 
 	/*
@@ -1273,7 +1273,7 @@ nd6_is_new_addr_neighbor(const struct sockaddr_in6 *addr, struct ifnet *ifp)
 		if (!(pr->ndpr_stateflags & NDPRF_ONLINK)) {
 
 			/* Always use the default FIB here. */
-			dst6 = (struct sockaddr *)&pr->ndpr_prefix;
+			dst6 = (const struct sockaddr *)&pr->ndpr_prefix;
 
 			/* Restore length field before retrying lookup */
 			rt_key.sin6_len = sizeof(rt_key);