diff --git a/sys/netinet/cc/cc_cubic.c b/sys/netinet/cc/cc_cubic.c
--- a/sys/netinet/cc/cc_cubic.c
+++ b/sys/netinet/cc/cc_cubic.c
@@ -88,6 +88,7 @@
 static void	cubic_newround(struct cc_var *ccv, uint32_t round_cnt);
 static void	cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt,
        uint32_t rxtcnt, uint32_t fas);
+static unsigned long	cubic_compute_pipe(struct cc_var *ccv);
 
 struct cc_algo cubic_cc_algo = {
 	.name = "cubic",
@@ -424,6 +425,7 @@
 static void
 cubic_cong_signal(struct cc_var *ccv, uint32_t type)
 {
+	unsigned long pipe;
 	struct cubic *cubic_data;
 	u_int mss;
 
@@ -456,10 +458,12 @@
 			cubic_log_hystart_event(ccv, cubic_data, 9, CCV(ccv, snd_ssthresh));
 		}
 		if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
+			pipe = cubic_compute_pipe(ccv);
 			cubic_ssthresh_update(ccv, mss);
+			CCV(ccv, snd_cwnd) = ulmax((pipe * CUBIC_BETA) >> CUBIC_SHIFT, 
+			    CCV(ccv, snd_ssthresh));
 			cubic_data->num_cong_events++;
 			cubic_data->t_epoch = 0; /* This will recalculate K */
-			CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
 			ENTER_CONGRECOVERY(CCV(ccv, t_flags));
 		}
 		break;
@@ -529,7 +533,7 @@
 cubic_post_recovery(struct cc_var *ccv)
 {
 	struct cubic *cubic_data;
-	int pipe;
+	unsigned long pipe;
 
 	cubic_data = ccv->cc_data;
 	pipe = 0;
@@ -542,10 +546,7 @@
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_newsack)
-			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
-		else
-			pipe = CCV(ccv, snd_max) - ccv->curack;
+		pipe = cubic_compute_pipe(ccv);
 
 		if (pipe < CCV(ccv, snd_ssthresh))
 			/*
@@ -627,11 +628,16 @@
 	struct cubic *cubic_data;
 	uint32_t ssthresh;
 	uint32_t cwnd;
+	unsigned long pipe;
 
 	cubic_data = ccv->cc_data;
 	cwnd = CCV(ccv, snd_cwnd);
+	cubic_data->cwnd_prior = cwnd;
 
-	/* Fast convergence heuristic. */
+	/*
+	 * draft-ietf-tcpm-rfc8312bis-15 Section 4.7:
+	 * Fast convergence heuristic
+	 */
 	if (cwnd < cubic_data->W_max) {
 		cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT;
 	}
@@ -639,19 +645,11 @@
 	cubic_data->W_max = cwnd;
 
 	/*
-	 * On the first congestion event, set ssthresh to cwnd * 0.5
-	 * and reduce W_max to cwnd * beta. This aligns the cubic concave
-	 * region appropriately. On subsequent congestion events, set
-	 * ssthresh to cwnd * beta.
+	 * draft-ietf-tcpm-rfc8312bis-15 Section 4.6:
+	 * Calculate the ssthresh using the outstanding unacknowledged data
 	 */
-	if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) {
-		ssthresh = cwnd >> 1;
-		cubic_data->W_max = ((uint64_t)cwnd *
-		    CUBIC_BETA) >> CUBIC_SHIFT;
-	} else {
-		ssthresh = ((uint64_t)cwnd *
-		    CUBIC_BETA) >> CUBIC_SHIFT;
-	}
+	pipe = cubic_compute_pipe(ccv);
+	ssthresh = (pipe * CUBIC_BETA) >> CUBIC_SHIFT;
 	CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg);
 }
 
@@ -730,5 +728,17 @@
 		cubic_log_hystart_event(ccv, cubicd, 4, round_cnt);
 }
 
+static unsigned long
+cubic_compute_pipe(struct cc_var *ccv)
+{
+	unsigned long pipe;
+
+	if (V_tcp_do_newsack)
+		pipe = tcp_compute_pipe(ccv->ccvc.tcp);
+	else
+		pipe = CCV(ccv, snd_max) - ccv->curack;
+	return pipe;
+}
+
 DECLARE_CC_MODULE(cubic, &cubic_cc_algo);
 MODULE_VERSION(cubic, 2);