diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
index eda02d9c3293..d6679034a576 100644
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -2900,14 +2900,6 @@ ip6_mloopback(struct ifnet *ifp, struct mbuf *m, struct sockaddr_in6 *dst)
 		if (copym == NULL)
 			return;
 	}
-
-#ifdef DIAGNOSTIC
-	if (copym->m_len < sizeof(*ip6)) {
-		m_freem(copym);
-		return;
-	}
-#endif
-
 	ip6 = mtod(copym, struct ip6_hdr *);
 	/*
 	 * clear embedded scope identifiers if necessary.
@@ -2915,7 +2907,11 @@ ip6_mloopback(struct ifnet *ifp, struct mbuf *m, struct sockaddr_in6 *dst)
 	 */
 	in6_clearscope(&ip6->ip6_src);
 	in6_clearscope(&ip6->ip6_dst);
-
+	if (copym->m_pkthdr.csum_flags & CSUM_DELAY_DATA_IPV6) {
+		copym->m_pkthdr.csum_flags |= CSUM_DATA_VALID_IPV6 |
+		    CSUM_PSEUDO_HDR;
+		copym->m_pkthdr.csum_data = 0xffff;
+	}
 	(void)if_simloop(ifp, copym, dst->sin6_family, 0);
 }