Index: sys/netinet/tcp_subr.c
===================================================================
--- sys/netinet/tcp_subr.c	(revision 292681)
+++ sys/netinet/tcp_subr.c	(working copy)
@@ -835,7 +835,7 @@ void
 tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
     tcp_seq ack, tcp_seq seq, int flags)
 {
-	int tlen;
+	int tlen, optlen = 0;
 	int win = 0;
 	struct ip *ip;
 	struct tcphdr *nth;
@@ -845,6 +845,7 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct
 #endif /* INET6 */
 	int ipflags = 0;
 	struct inpcb *inp;
+	struct tcpopt to;
 
 	KASSERT(tp != NULL || m != NULL, ("tcp_respond: tp and m both NULL"));
 
@@ -943,6 +944,17 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct
 			ip->ip_off |= htons(IP_DF);
 	}
 #endif
+	if (tp != NULL) {
+		to.to_flags = 0;
+		if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
+		    (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
+			to.to_flags |= TOF_TS;
+			to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
+			to.to_tsecr = tp->ts_recent;
+			tlen += optlen = tcp_addoptions(&to,
+			    (u_char *)(nth + 1));
+		}
+	}
 	m->m_len = tlen;
 	m->m_pkthdr.len = tlen;
 	m->m_pkthdr.rcvif = NULL;
@@ -965,7 +977,7 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct
 	nth->th_seq = htonl(seq);
 	nth->th_ack = htonl(ack);
 	nth->th_x2 = 0;
-	nth->th_off = sizeof (struct tcphdr) >> 2;
+	nth->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
 	nth->th_flags = flags;
 	if (tp != NULL)
 		nth->th_win = htons((u_short) (win >> tp->rcv_scale));