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
@@ -4060,9 +4060,13 @@
 int
 tcp_compute_pipe(struct tcpcb *tp)
 {
-	return (tp->snd_max - tp->snd_una +
-		tp->sackhint.sack_bytes_rexmit -
-		tp->sackhint.sacked_bytes);
+	if (tp->t_fb->tfb_compute_pipe == NULL) {
+		return (tp->snd_max - tp->snd_una +
+			tp->sackhint.sack_bytes_rexmit -
+			tp->sackhint.sacked_bytes);
+	} else {
+		return((*tp->t_fb->tfb_compute_pipe)(tp));
+	}
 }
 
 uint32_t
diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c
--- a/sys/netinet/tcp_stacks/rack.c
+++ b/sys/netinet/tcp_stacks/rack.c
@@ -9397,6 +9397,20 @@
 	return (was_tlp);
 }
 
+static uint32_t
+do_rack_compute_pipe(struct tcpcb *tp, struct tcp_rack *rack, uint32_t snd_una)
+{
+	return (((tp->snd_max - snd_una) - rack->r_ctl.rc_sacked) + rack->r_ctl.rc_holes_rxt);
+}
+
+static int32_t
+rack_compute_pipe(struct tcpcb *tp)
+{
+	return ((int32_t)do_rack_compute_pipe(tp,
+					      (struct tcp_rack *)tp->t_fb_ptr,
+					      tp->snd_una));
+}
+
 static void
 rack_update_prr(struct tcpcb *tp, struct tcp_rack *rack, uint32_t changed, tcp_seq th_ack)
 {
@@ -9421,7 +9435,7 @@
 	} else {
 		snd_una = th_ack;
 	}
-	pipe = ((tp->snd_max - snd_una) - rack->r_ctl.rc_sacked) + rack->r_ctl.rc_holes_rxt;
+	pipe = do_rack_compute_pipe(tp, rack, snd_una);
 	if (pipe > tp->snd_ssthresh) {
 		long sndcnt;
 
@@ -20317,6 +20331,7 @@
 	.tfb_tcp_mtu_chg = rack_mtu_change,
 	.tfb_pru_options = rack_pru_options,
 	.tfb_hwtls_change = rack_hw_tls_change,
+	.tfb_compute_pipe = rack_compute_pipe,
 	.tfb_flags = TCP_FUNC_OUTPUT_CANDROP,
 };
 
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
@@ -375,6 +375,7 @@
 	void	(*tfb_tcp_mtu_chg)(struct tcpcb *);
 	int	(*tfb_pru_options)(struct tcpcb *, int);
 	void	(*tfb_hwtls_change)(struct tcpcb *, int);
+	int     (*tfb_compute_pipe)(struct tcpcb *tp);
 	volatile uint32_t tfb_refcnt;
 	uint32_t  tfb_flags;
 	uint8_t	tfb_id;