diff --git a/sys/netinet/ip_reass.c b/sys/netinet/ip_reass.c
index fbf9c176956d..6e83800ee7ea 100644
--- a/sys/netinet/ip_reass.c
+++ b/sys/netinet/ip_reass.c
@@ -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);
 	}
 	/*
diff --git a/sys/netinet6/frag6.c b/sys/netinet6/frag6.c
index 0384c7fdc80d..3b2773f812f8 100644
--- a/sys/netinet6/frag6.c
+++ b/sys/netinet6/frag6.c
@@ -541,6 +541,7 @@ frag6_input(struct mbuf **mp, int *offp, int proto)
 		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;