diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -328,13 +328,16 @@
 				 */
 				p = NULL;
 				goto after_sack_rexmit;
-			} else
+			} else {
 				/* Can rexmit part of the current hole */
 				len = ((int32_t)ulmin(cwin,
-						   tp->snd_recover - p->rxmit));
-		} else
-			len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
-		off = p->rxmit - tp->snd_una;
+				    SEQ_SUB(tp->snd_recover, p->rxmit)));
+			}
+		} else {
+			len = ((int32_t)ulmin(cwin,
+			    SEQ_SUB(p->end, p->rxmit)));
+		}
+		off = SEQ_SUB(p->rxmit, tp->snd_una);
 		KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 		    __func__, off));
 		if (len > 0) {
diff --git a/sys/netinet/tcp_seq.h b/sys/netinet/tcp_seq.h
--- a/sys/netinet/tcp_seq.h
+++ b/sys/netinet/tcp_seq.h
@@ -43,6 +43,7 @@
 #define	SEQ_LEQ(a,b)	((int)((a)-(b)) <= 0)
 #define	SEQ_GT(a,b)	((int)((a)-(b)) > 0)
 #define	SEQ_GEQ(a,b)	((int)((a)-(b)) >= 0)
+#define	SEQ_SUB(a,b)	((int)((a)-(b)))
 
 #define	SEQ_MIN(a, b)	((SEQ_LT(a, b)) ? (a) : (b))
 #define	SEQ_MAX(a, b)	((SEQ_GT(a, b)) ? (a) : (b))