diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -527,10 +527,16 @@
 		}
 
 		NET_EPOCH_ENTER(et);
-		syncache_respond(sc, NULL, TH_SYN|TH_ACK);
+		if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) {
+			syncache_timeout(sc, sch, 0);
+			TCPSTAT_INC(tcps_sndacks);
+			TCPSTAT_INC(tcps_sndtotal);
+			TCPSTAT_INC(tcps_sc_retransmitted);
+		} else {
+			syncache_drop(sc, sch);
+			TCPSTAT_INC(tcps_sc_dropped);
+		}
 		NET_EPOCH_EXIT(et);
-		TCPSTAT_INC(tcps_sc_retransmitted);
-		syncache_timeout(sc, sch, 0);
 	}
 	if (!TAILQ_EMPTY(&(sch)->sch_bucket))
 		callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
@@ -688,7 +694,13 @@
 				    "sending challenge ACK\n",
 				    s, __func__,
 				    th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
-			syncache_respond(sc, m, TH_ACK);
+			if (syncache_respond(sc, m, TH_ACK) == 0) {
+				TCPSTAT_INC(tcps_sndacks);
+				TCPSTAT_INC(tcps_sndtotal);
+			} else {
+				syncache_drop(sc, sch);
+				TCPSTAT_INC(tcps_sc_dropped);
+			}
 		}
 	} else {
 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
@@ -1549,6 +1561,9 @@
 			syncache_timeout(sc, sch, 1);
 			TCPSTAT_INC(tcps_sndacks);
 			TCPSTAT_INC(tcps_sndtotal);
+		} else {
+			syncache_drop(sc, sch);
+			TCPSTAT_INC(tcps_sc_dropped);
 		}
 		SCH_UNLOCK(sch);
 		goto donenoprobe;