Index: sys/netgraph/ng_l2tp.c
===================================================================
--- sys/netgraph/ng_l2tp.c	(revision 316739)
+++ sys/netgraph/ng_l2tp.c	(working copy)
@@ -994,6 +994,11 @@ ng_l2tp_rcvdata_lower(hook_p h, item_p item)
 		ERROUT(0);
 	}
 
+	/* Clear any h/w csum flags as they are no longer valid. */
+	if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID)
+		m->m_pkthdr.csum_flags &= ~(CSUM_DATA_VALID |
+		    CSUM_PSEUDO_HDR);
+
 	/* Deliver data */
 	NG_FWD_NEW_DATA(error, item, hook, m);
 done: