diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 2f7daf88434a..5080ccf830f3 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: tcp_subr.c,v 1.47 1998/04/13 21:18:19 kml Exp $	*/
+/*	$NetBSD: tcp_subr.c,v 1.48 1998/04/29 05:16:46 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
@@ -111,6 +111,11 @@ int 	tcp_rttdflt = TCPTV_SRTTDFLT / PR_SLOWHZ;
 int	tcp_do_rfc1323 = 1;
 int	tcp_init_win = 1;
 int	tcp_mss_ifmtu = 0;
+#ifdef TCP_COMPAT_42
+int	tcp_compat_42 = 1;
+#else
+int	tcp_compat_42 = 0;
+#endif
 
 #ifndef TCBHASHSIZE
 #define	TCBHASHSIZE	128
@@ -204,11 +209,12 @@ tcp_respond(tp, ti, m, ack, seq, flags)
 		m = m_gethdr(M_DONTWAIT, MT_HEADER);
 		if (m == NULL)
 			return (ENOBUFS);
-#ifdef TCP_COMPAT_42
-		tlen = 1;
-#else
-		tlen = 0;
-#endif
+
+		if (tcp_compat_42)
+			tlen = 1;
+		else
+			tlen = 0;
+
 		m->m_data += max_linkhdr;
 		*mtod(m, struct tcpiphdr *) = *ti;
 		ti = mtod(m, struct tcpiphdr *);
@@ -830,13 +836,14 @@ tcp_new_iss(tp, len, addin)
 #endif
 	}
 
-#ifdef TCP_COMPAT_42
-	/*
-	 * limit it to the positive range for really old TCP implementations
-	 */
-	if ((int)tcp_iss < 0)
-		tcp_iss &= 0x7fffffff;		/* XXX */
-#endif
+	if (tcp_compat_42) {
+		/*
+		 * Limit it to the positive range for really old TCP
+		 * implementations.
+		 */
+		if ((int)tcp_iss < 0)
+			tcp_iss &= 0x7fffffff;		/* XXX */
+	}
 
 	return tcp_iss;
 }
@@ -861,5 +868,3 @@ tcp_optlen(tp)
 	else
 		return 0;
 }
-
-
diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c
index c55b1b6c4db2..fd05a9868002 100644
--- a/sys/netinet/tcp_timer.c
+++ b/sys/netinet/tcp_timer.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: tcp_timer.c,v 1.33 1998/04/29 03:44:12 kml Exp $	*/
+/*	$NetBSD: tcp_timer.c,v 1.34 1998/04/29 05:16:47 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
@@ -72,8 +72,6 @@
  *	@(#)tcp_timer.c	8.2 (Berkeley) 5/24/95
  */
 
-#include "opt_tcp_compat_42.h"
-
 #ifndef TUBA_INCLUDE
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -185,10 +183,9 @@ tpgone:
 	}
 #if NRND == 0 /* Do we need to do this when using random() ? */
 	tcp_iss_seq += TCP_ISSINCR;			/* increment iss */
-#ifdef TCP_COMPAT_42
-	if ((int)tcp_iss_seq < 0)
-		tcp_iss_seq = 0;			/* XXX */
-#endif
+	if (tcp_compat_42)
+		if ((int)tcp_iss_seq < 0)
+			tcp_iss_seq = 0;		/* XXX */
 #endif
 	tcp_now++;					/* for timestamps */
 	if (++syn_cache_last >= tcp_syn_cache_interval) {
@@ -391,19 +388,19 @@ tcp_timers(tp, timer)
 			 * correspondent TCP to respond.
 			 */
 			tcpstat.tcps_keepprobe++;
-#ifdef TCP_COMPAT_42
-			/*
-			 * The keepalive packet must have nonzero length
-			 * to get a 4.2 host to respond.
-			 */
-			(void)tcp_respond(tp, tp->t_template,
-			    (struct mbuf *)NULL, tp->rcv_nxt - 1,
-			    tp->snd_una - 1, 0);
-#else
-			(void)tcp_respond(tp, tp->t_template,
-			    (struct mbuf *)NULL, tp->rcv_nxt,
-			    tp->snd_una - 1, 0);
-#endif
+			if (tcp_compat_42) {
+				/*
+				 * The keepalive packet must have nonzero
+				 * length to get a 4.2 host to respond.
+				 */
+				(void)tcp_respond(tp, tp->t_template,
+				    (struct mbuf *)NULL, tp->rcv_nxt - 1,
+				    tp->snd_una - 1, 0);
+			} else {
+				(void)tcp_respond(tp, tp->t_template,
+				    (struct mbuf *)NULL, tp->rcv_nxt,
+				    tp->snd_una - 1, 0);
+			}
 			tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
 		} else
 			tp->t_timer[TCPT_KEEP] = tcp_keepidle;
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index ffce19848d55..47b4e5a19b93 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: tcp_var.h,v 1.41 1998/04/13 21:18:20 kml Exp $	*/
+/*	$NetBSD: tcp_var.h,v 1.42 1998/04/29 05:16:47 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
@@ -397,6 +397,7 @@ extern	int tcp_do_rfc1323;	/* enabled/disabled? */
 extern	int tcp_mssdflt;	/* default seg size */
 extern	int tcp_init_win;	/* initial window */
 extern	int tcp_mss_ifmtu;	/* take MSS from interface, not in_maxmtu */
+extern	int tcp_compat_42;	/* work around ancient broken TCP peers */
 extern	int tcp_syn_cache_limit; /* max entries for compressed state engine */
 extern	int tcp_syn_bucket_limit;/* max entries per hash bucket */
 extern	int tcp_syn_cache_interval; /* compressed state timer */