Index: sys/netinet/tcp_input.c
===================================================================
RCS file: /mount/openbsd/cvs/src/sys/netinet/tcp_input.c,v
retrieving revision 1.368
diff -u -p -u -p -r1.368 tcp_input.c
--- sys/netinet/tcp_input.c	16 Apr 2021 12:08:25 -0000	1.368
+++ sys/netinet/tcp_input.c	20 Jul 2021 15:58:33 -0000
@@ -176,8 +176,7 @@ do { \
 	struct ifnet *ifp = NULL; \
 	if (m && (m->m_flags & M_PKTHDR)) \
 		ifp = if_get(m->m_pkthdr.ph_ifidx); \
-	if (TCP_TIMER_ISARMED(tp, TCPT_DELACK) || \
-	    (tcp_ack_on_push && (tiflags) & TH_PUSH) || \
+	if ((tcp_ack_on_push && (tiflags) & TH_PUSH) || \
 	    (ifp && (ifp->if_flags & IFF_LOOPBACK))) \
 		tp->t_flags |= TF_ACKNOW; \
 	else \
Index: sys/netinet/tcp_output.c
===================================================================
RCS file: /mount/openbsd/cvs/src/sys/netinet/tcp_output.c,v
retrieving revision 1.130
diff -u -p -u -p -r1.130 tcp_output.c
--- sys/netinet/tcp_output.c	8 Feb 2021 19:37:15 -0000	1.130
+++ sys/netinet/tcp_output.c	20 Jul 2021 15:58:33 -0000
@@ -398,6 +398,8 @@ again:
 			goto send;
 		if (2 * adv >= (long) so->so_rcv.sb_hiwat)
 			goto send;
+		if (so->so_rcv.sb_cc == 0)
+			goto send;
 	}
 
 	/*