diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -785,7 +785,7 @@
 
 		/*
 		 * Record statistics for this interface address.
-		 * With CSUM_TSO the byte/packet count will be slightly
+		 * With TSO the byte/packet count will be slightly
 		 * incorrect because we count the IP+TCP headers only
 		 * once instead of for every generated packet.
 		 */
@@ -814,9 +814,9 @@
 		goto done;
 	}
 
-	/* Balk when DF bit is set or the interface didn't support TSO. */
+	/* Balk when DF bit is set or the interface didn't support offloading. */
 	if ((ip_off & IP_DF) ||
-	    (m->m_pkthdr.csum_flags & (CSUM_TSO | CSUM_INNER_TSO))) {
+	    (m->m_pkthdr.csum_flags & CSUM_TX_DONT_FRAG)) {
 		error = EMSGSIZE;
 		IPSTAT_INC(ips_cantfrag);
 		goto bad;
diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -1142,7 +1142,8 @@
 	/* XXX-BZ m->m_pkthdr.csum_flags &= ~ifp->if_hwassist; */
 	tlen = m->m_pkthdr.len;
 
-	if ((opt && (opt->ip6po_flags & IP6PO_DONTFRAG)) || tso)
+	if ((opt && (opt->ip6po_flags & IP6PO_DONTFRAG) != 0) ||
+	    (m->m_pkthdr.csum_flags & CSUM_TX_DONT_FRAG) != 0)
 		dontfrag = 1;
 	else
 		dontfrag = 0;
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -712,6 +712,15 @@
 #define	CSUM_UDP_IPV6		CSUM_IP6_UDP
 #define	CSUM_TCP_IPV6		CSUM_IP6_TCP
 #define	CSUM_SCTP_IPV6		CSUM_IP6_SCTP
+#define	CSUM_TX_DONT_FRAG	\
+  (CSUM_TSO|			\
+   CSUM_INNER_IP|		\
+   CSUM_INNER_IP_UDP|		\
+   CSUM_INNER_IP_TCP|		\
+   CSUM_INNER_IP_TSO|		\
+   CSUM_INNER_IP6_UDP|		\
+   CSUM_INNER_IP6_TCP|		\
+   CSUM_INNER_IP6_TSO)
 
 /*
  * mbuf types describing the content of the mbuf (including external storage).