diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -3979,6 +3979,8 @@
 		tp->t_tsomax = cap.tsomax;
 		tp->t_tsomaxsegcount = cap.tsomaxsegcount;
 		tp->t_tsomaxsegsize = cap.tsomaxsegsize;
+		if (cap.ipsec_tso)
+			tp->t_flags2 |= TF2_IPSEC_TSO;
 	}
 }
 
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -201,9 +201,7 @@
 	struct tcphdr *th;
 	u_char opt[TCP_MAXOLEN];
 	unsigned ipoptlen, optlen, hdrlen, ulen;
-#if defined(IPSEC) || defined(IPSEC_SUPPORT)
 	unsigned ipsec_optlen = 0;
-#endif
 	int idle, sendalot, curticks;
 	int sack_rxmit, sack_bytes_rxmt;
 	struct sackhole *p;
@@ -553,15 +551,15 @@
 				offsetof(struct ipoption, ipopt_list);
 	else
 		ipoptlen = 0;
-#if defined(IPSEC) || defined(IPSEC_SUPPORT)
 	ipoptlen += ipsec_optlen;
-#endif
 
 	if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 	    (tp->t_port == 0) &&
 	    ((tp->t_flags & TF_SIGNATURE) == 0) &&
 	    tp->rcv_numsacks == 0 && ((sack_rxmit == 0) || V_tcp_sack_tso) &&
-	    ipoptlen == 0 && !(flags & TH_SYN))
+	    (ipoptlen == 0 || (ipoptlen == ipsec_optlen &&
+	    (tp->t_flags2 & TF2_IPSEC_TSO) != 0)) &&
+	    !(flags & TH_SYN))
 		tso = 1;
 
 	if (SEQ_LT((sack_rxmit ? p->rxmit : tp->snd_nxt) + len,
@@ -917,7 +915,7 @@
 			 * overflowing or exceeding the maximum length
 			 * allowed by the network interface:
 			 */
-			KASSERT(ipoptlen == 0,
+			KASSERT(ipoptlen ==  ipsec_optlen,
 			    ("%s: TSO can't do IP options", __func__));
 
 			/*
@@ -926,8 +924,8 @@
 			 */
 			if (if_hw_tsomax != 0) {
 				/* compute maximum TSO length */
-				max_len = (if_hw_tsomax - hdrlen -
-				    max_linkhdr);
+				max_len = if_hw_tsomax - hdrlen -
+				    ipsec_optlen - max_linkhdr;
 				if (max_len <= 0) {
 					len = 0;
 				} else if (len > max_len) {
@@ -941,7 +939,7 @@
 			 * fractional unless the send sockbuf can be
 			 * emptied:
 			 */
-			max_len = (tp->t_maxseg - optlen);
+			max_len = tp->t_maxseg - optlen - ipsec_optlen;
 			if (((uint32_t)off + (uint32_t)len) <
 			    sbavail(&so->so_snd)) {
 				moff = len % max_len;
@@ -1393,10 +1391,10 @@
 	 * The TCP pseudo header checksum is always provided.
 	 */
 	if (tso) {
-		KASSERT(len > tp->t_maxseg - optlen,
+		KASSERT(len > tp->t_maxseg - optlen - ipsec_optlen,
 		    ("%s: len <= tso_segsz", __func__));
 		m->m_pkthdr.csum_flags |= CSUM_TSO;
-		m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
+		m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen - ipsec_optlen;
 	}
 
 	KASSERT(len + hdrlen == m_length(m, NULL),
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -3338,6 +3338,9 @@
 				cap->tsomax = ifp->if_hw_tsomax;
 				cap->tsomaxsegcount = ifp->if_hw_tsomaxsegcount;
 				cap->tsomaxsegsize = ifp->if_hw_tsomaxsegsize;
+				/* XXXKIB IFCAP2_IPSEC_ACCEL_TSO */
+				cap->ipsec_tso =  (ifp->if_capenable2 &
+				    IFCAP2_BIT(IFCAP2_IPSEC_ACCEL)) != 0;
 			}
 		}
 	}
@@ -3377,6 +3380,7 @@
 				cap->tsomax = ifp->if_hw_tsomax;
 				cap->tsomaxsegcount = ifp->if_hw_tsomaxsegcount;
 				cap->tsomaxsegsize = ifp->if_hw_tsomaxsegsize;
+				cap->ipsec_tso = false; /* XXXKIB */
 			}
 		}
 	}
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -847,6 +847,7 @@
 #define	TF2_DONT_SACK_QUEUE	0x00040000 /* Don't wake on sack */
 #define	TF2_CANNOT_DO_ECN	0x00080000 /* The stack does not do ECN */
 #define TF2_PROC_SACK_PROHIBIT	0x00100000 /* Due to small MSS size do not process sack's */
+#define	TF2_IPSEC_TSO		0x00200000	/* IPSEC + TSO supported */
 
 /*
  * Structure to hold TCP options that are only used during segment
@@ -1433,6 +1434,7 @@
 	u_int	tsomax;
 	u_int	tsomaxsegcount;
 	u_int	tsomaxsegsize;
+	bool	ipsec_tso;
 };
 uint32_t tcp_maxmtu(struct in_conninfo *, struct tcp_ifcap *);
 uint32_t tcp_maxmtu6(struct in_conninfo *, struct tcp_ifcap *);