--- netinet/tcp_output.c.sav	2015-08-22 07:48:12.000000000 -0400
+++ netinet/tcp_output.c	2015-08-22 07:50:52.000000000 -0400
@@ -794,7 +794,13 @@ send:
 
 			/* extract TSO information */
 			if_hw_tsomax = tp->t_tsomax;
-			if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
+			/*
+			 * Subtract 1 for the tcp/ip header mbuf that
+			 * will be prepended to this mbuf chain after
+			 * the code in this section limits the number of
+			 * mbufs in the chain to if_hw_tsomaxsegcount.
+			 */
+			if_hw_tsomaxsegcount = tp->t_tsomaxsegcount - 1;
 			if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 
 			/*