diff -r fc8f3985a31e -r 65a8d6addca3 sys/netinet/ip_reass.c
--- a/sys/netinet/ip_reass.c	Tue Dec 26 11:08:30 2017 -0800
+++ b/sys/netinet/ip_reass.c	Tue Dec 26 21:00:47 2017 -0800
@@ -377,6 +377,7 @@ ip_reass(struct mbuf *m)
 		q->m_nextpkt = NULL;
 		m->m_pkthdr.csum_flags &= q->m_pkthdr.csum_flags;
 		m->m_pkthdr.csum_data += q->m_pkthdr.csum_data;
+		m_demote_pkthdr(q);
 		m_cat(m, q);
 	}
 	/*