Index: sys/netinet/tcp_timer.c
===================================================================
--- sys/netinet/tcp_timer.c
+++ sys/netinet/tcp_timer.c
@@ -679,11 +679,16 @@
 			 * - Reduce MTU to lower value than what we
 			 *   negotiated with peer.
 			 */
-			/* Record that we may have found a black hole. */
-			tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
+			if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) == 0) {
+				/*
+				 * Record that we may have found a black
+				 * hole.
+				 */
+				tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
 
-			/* Keep track of previous MSS. */
-			tp->t_pmtud_saved_maxseg = tp->t_maxseg;
+				/* Keep track of previous MSS. */
+				tp->t_pmtud_saved_maxseg = tp->t_maxseg;
+			}
 
 			/* 
 			 * Reduce the MSS to blackhole value or to the default