diff --git a/sys/netinet6/in6.c b/sys/netinet6/in6.c
index d5a8e159c96..a88fed9f6ef 100644
--- a/sys/netinet6/in6.c
+++ b/sys/netinet6/in6.c
@@ -586,7 +586,7 @@ in6_control(so, cmd, data, ifp, td)
 			 * signed.
 			 */
 			maxexpire = (-1) &
-			    ~(1 << ((sizeof(maxexpire) * 8) - 1));
+			    ~((time_t)1 << ((sizeof(maxexpire) * 8) - 1));
 			if (ia->ia6_lifetime.ia6t_vltime <
 			    maxexpire - ia->ia6_updatetime) {
 				retlt->ia6t_expire = ia->ia6_updatetime +
@@ -604,7 +604,7 @@ in6_control(so, cmd, data, ifp, td)
 			 * signed.
 			 */
 			maxexpire = (-1) &
-			    ~(1 << ((sizeof(maxexpire) * 8) - 1));
+			    ~((time_t)1 << ((sizeof(maxexpire) * 8) - 1));
 			if (ia->ia6_lifetime.ia6t_pltime <
 			    maxexpire - ia->ia6_updatetime) {
 				retlt->ia6t_preferred = ia->ia6_updatetime +
diff --git a/sys/netinet6/nd6.c b/sys/netinet6/nd6.c
index da2a6170f38..4317b5b1870 100644
--- a/sys/netinet6/nd6.c
+++ b/sys/netinet6/nd6.c
@@ -1481,7 +1481,8 @@ nd6_ioctl(cmd, data, ifp)
 
 				/* XXX: we assume time_t is signed. */
 				maxexpire = (-1) &
-				    ~(1 << ((sizeof(maxexpire) * 8) - 1));
+				    ~((time_t)1 <<
+				    ((sizeof(maxexpire) * 8) - 1));
 				if (pr->ndpr_vltime <
 				    maxexpire - pr->ndpr_lastupdate) {
 					oprl->prefix[i].expire =
@@ -2330,7 +2331,8 @@ nd6_sysctl_prlist(SYSCTL_HANDLER_ARGS)
 
 				/* XXX: we assume time_t is signed. */
 				maxexpire = (-1) &
-				    ~(1 << ((sizeof(maxexpire) * 8) - 1));
+				    ~((time_t)1 <<
+				    ((sizeof(maxexpire) * 8) - 1));
 				if (pr->ndpr_vltime <
 				    maxexpire - pr->ndpr_lastupdate) {
 				    p->expire = pr->ndpr_lastupdate +