diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -699,6 +699,7 @@
 
 		case 0: /* Continue normally */
 			ip = mtod(m, struct ip *);
+			ip_len = ntohs(ip->ip_len);
 			break;
 
 		case -1: /* Need to try again */