diff --git a/sys/netinet6/in6.h b/sys/netinet6/in6.h
index f0cf4f42c99..f910e701b9f 100644
--- a/sys/netinet6/in6.h
+++ b/sys/netinet6/in6.h
@@ -632,7 +632,9 @@ struct ip6_mtuinfo {
 
 #ifdef _KERNEL
 struct cmsghdr;
+struct ip6_hdr;
 
+int	in6_cksum_pseudo(struct ip6_hdr *, uint32_t, uint8_t, uint16_t);
 int	in6_cksum __P((struct mbuf *, u_int8_t, u_int32_t, u_int32_t));
 int	in6_localaddr __P((struct in6_addr *));
 int	in6_localip(struct in6_addr *);
diff --git a/sys/netinet6/in6_cksum.c b/sys/netinet6/in6_cksum.c
index 034848b7db9..da8a2e6bf3c 100644
--- a/sys/netinet6/in6_cksum.c
+++ b/sys/netinet6/in6_cksum.c
@@ -80,6 +80,66 @@ __FBSDID("$FreeBSD$");
 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; (void)ADDCARRY(sum);}
 
+static int
+_in6_cksum_pseudo(struct ip6_hdr *ip6, uint32_t len, uint8_t nxt, uint16_t csum)
+{
+	int sum;
+	uint16_t scope, *w;
+	union {
+		u_int16_t phs[4];
+		struct {
+			u_int32_t	ph_len;
+			u_int8_t	ph_zero[3];
+			u_int8_t	ph_nxt;
+		} __packed ph;
+	} uph;
+
+	sum = csum;
+
+	/*
+	 * First create IP6 pseudo header and calculate a summary.
+	 */
+	uph.ph.ph_len = htonl(len);
+	uph.ph.ph_zero[0] = uph.ph.ph_zero[1] = uph.ph.ph_zero[2] = 0;
+	uph.ph.ph_nxt = nxt;
+
+	/* Payload length and upper layer identifier. */
+	sum += uph.phs[0];  sum += uph.phs[1];
+	sum += uph.phs[2];  sum += uph.phs[3];
+
+	/* IPv6 source address. */
+	scope = in6_getscope(&ip6->ip6_src);
+	w = (u_int16_t *)&ip6->ip6_src;
+	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
+	sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
+	if (scope != 0)
+		sum -= scope;
+
+	/* IPv6 destination address. */
+	scope = in6_getscope(&ip6->ip6_dst);
+	w = (u_int16_t *)&ip6->ip6_dst;
+	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
+	sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
+	if (scope != 0)
+		sum -= scope;
+
+	return (sum);
+}
+
+int
+in6_cksum_pseudo(struct ip6_hdr *ip6, uint32_t len, uint8_t nxt, uint16_t csum)
+{
+	int sum;
+	union {
+		u_int16_t s[2];
+		u_int32_t l;
+	} l_util;
+
+	sum = _in6_cksum_pseudo(ip6, len, nxt, csum);
+	REDUCE;
+	return (sum);
+}
+
 /*
  * m MUST contain a contiguous IP6 header.
  * off is an offset where TCP/UDP/ICMP6 header starts.