diff --git a/sys/netinet6/in6.c b/sys/netinet6/in6.c
index b2b3c64d0a7..fb661ade438 100644
--- a/sys/netinet6/in6.c
+++ b/sys/netinet6/in6.c
@@ -1034,6 +1034,15 @@ in6_alloc_ifa(struct ifnet *ifp, struct in6_aliasreq *ifra, int flags)
 	return (ia);
 }
 
+time_t
+in6_expire_time(uint32_t ltime)
+{
+	if (ltime == ND6_INFINITE_LIFETIME)
+		return (0);
+	else
+		return (time_uptime + ltime);
+}
+
 /*
  * Update/configure interface address parameters:
  *
@@ -1056,16 +1065,10 @@ in6_update_ifa_internal(struct ifnet *ifp, struct in6_aliasreq *ifra,
 	 * these members for applications.
 	 */
 	ia->ia6_lifetime = ifra->ifra_lifetime;
-	if (ia->ia6_lifetime.ia6t_vltime != ND6_INFINITE_LIFETIME) {
-		ia->ia6_lifetime.ia6t_expire =
-		    time_uptime + ia->ia6_lifetime.ia6t_vltime;
-	} else
-		ia->ia6_lifetime.ia6t_expire = 0;
-	if (ia->ia6_lifetime.ia6t_pltime != ND6_INFINITE_LIFETIME) {
-		ia->ia6_lifetime.ia6t_preferred =
-		    time_uptime + ia->ia6_lifetime.ia6t_pltime;
-	} else
-		ia->ia6_lifetime.ia6t_preferred = 0;
+	ia->ia6_lifetime.ia6t_expire =
+	    in6_expire_time(ifra->ifra_lifetime.ia6t_vltime);
+	ia->ia6_lifetime.ia6t_preferred =
+	    in6_expire_time(ifra->ifra_lifetime.ia6t_pltime);
 
 	/*
 	 * backward compatibility - if IN6_IFF_DEPRECATED is set from the
@@ -1323,6 +1326,28 @@ in6_addifaddr(struct ifnet *ifp, struct in6_aliasreq *ifra, struct in6_ifaddr *i
 				(*carp_detach_p)(&ia->ia_ifa, false);
 			goto out;
 		}
+	} else if (pr->ndpr_raf_onlink) {
+		time_t expiry;
+
+		/*
+		 * If the prefix already exists, update lifetimes, but avoid
+		 * shortening them.
+		 */
+		ND6_WLOCK();
+		expiry = in6_expire_time(pr0.ndpr_pltime);
+		if (pr->ndpr_preferred != 0 &&
+		    (pr->ndpr_preferred < expiry || expiry == 0)) {
+			pr->ndpr_pltime = pr0.ndpr_pltime;
+			pr->ndpr_preferred = expiry;
+		}
+		expiry = in6_expire_time(pr0.ndpr_vltime);
+		if (pr->ndpr_expire != 0 &&
+		    (pr->ndpr_expire < expiry || expiry == 0)) {
+			pr->ndpr_vltime = pr0.ndpr_vltime;
+			pr->ndpr_expire = expiry;
+		}
+		pr->ndpr_lastupdate = time_uptime;
+		ND6_WUNLOCK();
 	}
 
 	/* relate the address to the prefix */
diff --git a/sys/netinet6/in6.h b/sys/netinet6/in6.h
index 711c9b6d51c..3b543e0e058 100644
--- a/sys/netinet6/in6.h
+++ b/sys/netinet6/in6.h
@@ -671,6 +671,8 @@ int	in6_cksum_partial_l2(struct mbuf *m, uint8_t nxt, uint32_t off_l3,
 	    uint32_t off_l4, uint32_t len, uint32_t cov);
 int	in6_cksum_pseudo(struct ip6_hdr *, uint32_t, uint8_t, uint16_t);
 
+time_t	in6_expire_time(uint32_t);
+
 int	in6_localaddr(struct in6_addr *);
 int	in6_localip(struct in6_addr *);
 bool	in6_localip_fib(struct in6_addr *, uint16_t);
diff --git a/sys/netinet6/nd6_rtr.c b/sys/netinet6/nd6_rtr.c
index c145af7d3ff..18abb12e264 100644
--- a/sys/netinet6/nd6_rtr.c
+++ b/sys/netinet6/nd6_rtr.c
@@ -1139,39 +1139,18 @@ restart:
 	return (n);
 }
 
-static int
+static void
 in6_init_prefix_ltimes(struct nd_prefix *ndpr)
 {
-	if (ndpr->ndpr_pltime == ND6_INFINITE_LIFETIME)
-		ndpr->ndpr_preferred = 0;
-	else
-		ndpr->ndpr_preferred = time_uptime + ndpr->ndpr_pltime;
-	if (ndpr->ndpr_vltime == ND6_INFINITE_LIFETIME)
-		ndpr->ndpr_expire = 0;
-	else
-		ndpr->ndpr_expire = time_uptime + ndpr->ndpr_vltime;
-
-	return 0;
+	ndpr->ndpr_preferred = in6_expire_time(ndpr->ndpr_pltime);
+	ndpr->ndpr_expire = in6_expire_time(ndpr->ndpr_vltime);
 }
 
 static void
 in6_init_address_ltimes(struct nd_prefix *new, struct in6_addrlifetime *lt6)
 {
-	/* init ia6t_expire */
-	if (lt6->ia6t_vltime == ND6_INFINITE_LIFETIME)
-		lt6->ia6t_expire = 0;
-	else {
-		lt6->ia6t_expire = time_uptime;
-		lt6->ia6t_expire += lt6->ia6t_vltime;
-	}
-
-	/* init ia6t_preferred */
-	if (lt6->ia6t_pltime == ND6_INFINITE_LIFETIME)
-		lt6->ia6t_preferred = 0;
-	else {
-		lt6->ia6t_preferred = time_uptime;
-		lt6->ia6t_preferred += lt6->ia6t_pltime;
-	}
+	lt6->ia6t_preferred = in6_expire_time(lt6->ia6t_pltime);
+	lt6->ia6t_expire = in6_expire_time(lt6->ia6t_vltime);
 }
 
 static struct in6_ifaddr *
@@ -1355,11 +1334,8 @@ nd6_prelist_add(struct nd_prefixctl *pr, struct nd_defrouter *dr,
 	new->ndpr_vltime = pr->ndpr_vltime;
 	new->ndpr_pltime = pr->ndpr_pltime;
 	new->ndpr_flags = pr->ndpr_flags;
-	if ((error = in6_init_prefix_ltimes(new)) != 0) {
-		free(new, M_IP6NDP);
-		return (error);
-	}
 	new->ndpr_lastupdate = time_uptime;
+	in6_init_prefix_ltimes(new);
 
 	/* initialization */
 	LIST_INIT(&new->ndpr_advrtrs);
@@ -1502,7 +1478,7 @@ prelist_update(struct nd_prefixctl *new, struct nd_defrouter *dr,
 		if (new->ndpr_raf_onlink) {
 			pr->ndpr_vltime = new->ndpr_vltime;
 			pr->ndpr_pltime = new->ndpr_pltime;
-			(void)in6_init_prefix_ltimes(pr); /* XXX error case? */
+			in6_init_prefix_ltimes(pr);
 			pr->ndpr_lastupdate = time_uptime;
 		}