Index: sys/netinet/tcp_output.c
===================================================================
--- sys/netinet/tcp_output.c
+++ sys/netinet/tcp_output.c
@@ -1170,15 +1170,15 @@
 #endif
 				ip->ip_tos |= IPTOS_ECN_ECT0;
 			TCPSTAT_INC(tcps_ecn_ect0);
+			/*
+			 * Reply with proper ECN notifications.
+			 * Only set CWR on new data segments
+			 */
+			if (tp->t_flags2 & TF2_ECN_SND_CWR) {
+				flags |= TH_CWR;
+				tp->t_flags2 &= ~TF2_ECN_SND_CWR;
+			}
 		}
-		
-		/*
-		 * Reply with proper ECN notifications.
-		 */
-		if (tp->t_flags2 & TF2_ECN_SND_CWR) {
-			flags |= TH_CWR;
-			tp->t_flags2 &= ~TF2_ECN_SND_CWR;
-		} 
 		if (tp->t_flags2 & TF2_ECN_SND_ECE)
 			flags |= TH_ECE;
 	}