diff --git a/sys/netpfil/pf/pf.c b/sys/netpfil/pf/pf.c
--- a/sys/netpfil/pf/pf.c
+++ b/sys/netpfil/pf/pf.c
@@ -5571,11 +5571,17 @@
 	/* Copied from FreeBSD 10.0-CURRENT ip_output. */
 	m0->m_pkthdr.csum_flags |= CSUM_IP;
 	if (m0->m_pkthdr.csum_flags & CSUM_DELAY_DATA & ~ifp->if_hwassist) {
+		m0 = mb_unmapped_to_ext(m0);
+		if (m0 == NULL)
+			goto done;
 		in_delayed_cksum(m0);
 		m0->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA;
 	}
 #if defined(SCTP) || defined(SCTP_SUPPORT)
 	if (m0->m_pkthdr.csum_flags & CSUM_SCTP & ~ifp->if_hwassist) {
+		m0 = mb_unmapped_to_ext(m0);
+		if (m0 == NULL)
+			goto done;
 		sctp_delayed_cksum(m0, (uint32_t)(ip->ip_hl << 2));
 		m0->m_pkthdr.csum_flags &= ~CSUM_SCTP;
 	}
@@ -5752,6 +5758,9 @@
 	if (m0->m_pkthdr.csum_flags & CSUM_DELAY_DATA_IPV6 &
 	    ~ifp->if_hwassist) {
 		uint32_t plen = m0->m_pkthdr.len - sizeof(*ip6);
+		m0 = mb_unmapped_to_ext(m0);
+		if (m0 == NULL)
+			goto done;
 		in6_delayed_cksum(m0, plen, sizeof(struct ip6_hdr));
 		m0->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA_IPV6;
 	}