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
@@ -6685,6 +6685,7 @@
 	}
 	rack->r_ctl.rc_hpts_flags &= ~PACE_TMR_RXT;
 	rack->r_ctl.retran_during_recovery = 0;
+	rack->rc_ack_required = 1;
 	rack->r_ctl.dsack_byte_cnt = 0;
 	if (IN_FASTRECOVERY(tp->t_flags))
 		tp->t_flags |= TF_WASFRECOVERY;
@@ -14068,6 +14069,11 @@
 	 */
 	rack = (struct tcp_rack *)tp->t_fb_ptr;
 	if (m->m_flags & M_ACKCMP) {
+		/*
+		 * All compressed ack's are ack's by definition so
+		 * remove any ack required flag and then do the processing.
+		 */
+		rack->rc_ack_required = 0;
 		return (rack_do_compressed_ack_processing(tp, so, m, nxt_pkt, tv));
 	}
 	if (m->m_flags & M_ACKCMP) {
@@ -14238,6 +14244,9 @@
 		TCP_LOG_EVENTP(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_IN, 0,
 		    tlen, &log, true, &ltv);
 	}
+	/* Remove ack required flag if set, we have one  */
+	if (thflags & TH_ACK)
+		rack->rc_ack_required = 0;
 	if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
 		way_out = 4;
 		retval = 0;
@@ -16798,6 +16807,18 @@
 		}
 #ifdef TCP_ACCOUNTING
 		sched_unpin();
+#endif
+		return (0);
+	}
+	if ((rack->rc_ack_required == 1) &&
+	    (rack->r_timer_override == 0)){
+		/* A timeout occurred and no ack has arrived */
+		if (tcp_in_hpts(rack->rc_inp) == 0) {
+			/* Timer is not running */
+			rack_start_hpts_timer(rack, tp, cts, 0, 0, 0);
+		}
+#ifdef TCP_ACCOUNTING
+		sched_unpin();
 #endif
 		return (0);
 	}
diff --git a/sys/netinet/tcp_stacks/tcp_rack.h b/sys/netinet/tcp_stacks/tcp_rack.h
--- a/sys/netinet/tcp_stacks/tcp_rack.h
+++ b/sys/netinet/tcp_stacks/tcp_rack.h
@@ -549,7 +549,7 @@
 	struct inpcb *rc_inp;	/* The inpcb Lock(a) */
 	uint8_t rc_free_cnt;	/* Number of free entries on the rc_free list
 				 * Lock(a) */
-	uint8_t client_bufferlvl : 4, /* Expected range [0,5]: 0=unset, 1=low/empty */
+	uint8_t client_bufferlvl : 3, /* Expected range [0,5]: 0=unset, 1=low/empty */
 		rack_deferred_inited : 1,
 	        /* ******************************************************************** */
 	        /* Note for details of next two fields see rack_init_retransmit_rate()  */
@@ -557,6 +557,7 @@
 		full_size_rxt: 1,
 		shape_rxt_to_pacing_min : 1,
 	        /* ******************************************************************** */
+		rc_ack_required: 1,
 		spare : 1;
 	uint8_t no_prr_addback : 1,
 		gp_ready : 1,