Index: sys/netinet/ip_reass.c
===================================================================
--- sys/netinet/ip_reass.c
+++ sys/netinet/ip_reass.c
@@ -377,6 +377,7 @@
 		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);
 	}
 	/*
Index: sys/netinet6/frag6.c
===================================================================
--- sys/netinet6/frag6.c
+++ sys/netinet6/frag6.c
@@ -541,6 +541,7 @@
 		while (t->m_next)
 			t = t->m_next;
 		m_adj(IP6_REASS_MBUF(af6), af6->ip6af_offset);
+		m_demote_pkthdr(IP6_REASS_MBUF(af6));
 		m_cat(t, IP6_REASS_MBUF(af6));
 		free(af6, M_FTABLE);
 		af6 = af6dwn;