--- sys/dev/e1000/if_igb.c.orig	2014-01-09 16:33:39.000000000 +0100
+++ sys/dev/e1000/if_igb.c	2014-01-09 16:36:31.000000000 +0100
@@ -3883,6 +3883,7 @@
 			type_tucmd_mlhl |= E1000_ADVTXD_TUCMD_IPV4;
 			break;
 		case ETHERTYPE_IPV6:
+			KASSERT(ehdrlen + sizeof(struct ip6_hdr) <= mp->m_len, ("Ethernet and IPv6 header not contiguous"));
 			ip6 = (struct ip6_hdr *)(mp->m_data + ehdrlen);
 			ip_hlen = sizeof(struct ip6_hdr);
 			/* XXX-BZ this will go badly in case of ext hdrs. */