Index: sys/amd64/amd64/in_cksum.c
===================================================================
--- sys/amd64/amd64/in_cksum.c
+++ sys/amd64/amd64/in_cksum.c
@@ -192,43 +192,39 @@
 	return (sum);
 }
 
+struct cksum_cb_args {
+	uint64_t csum;
+	int clen;
+};
+
+static int
+in_cksum_cb(void *arg, void *data, u_int len)
+{
+	struct cksum_cb_args *a;
+
+	a = arg;
+	if (((uintptr_t)data ^ a->clen) & 1)
+		a->csum += in_cksumdata(data, len) << 8;
+	else
+		a->csum += in_cksumdata(data, len);
+	a->clen += len;
+	return (0);
+}
+
 u_short
 in_cksum_skip(struct mbuf *m, int len, int skip)
 {
-	u_int64_t sum = 0;
-	int mlen = 0;
-	int clen = 0;
-	caddr_t addr;
+	struct cksum_cb_args a;
 	union q_util q_util;
 	union l_util l_util;
+	uint64_t sum;
 
-        len -= skip;
-        for (; skip && m; m = m->m_next) {
-                if (m->m_len > skip) {
-                        mlen = m->m_len - skip;
-			addr = mtod(m, caddr_t) + skip;
-                        goto skip_start;
-                } else {
-                        skip -= m->m_len;
-                }
-        }
-
-	for (; m && len; m = m->m_next) {
-		if (m->m_len == 0)
-			continue;
-		mlen = m->m_len;
-		addr = mtod(m, caddr_t);
-skip_start:
-		if (len < mlen)
-			mlen = len;
-		if ((clen ^ (long) addr) & 1)
-		    sum += in_cksumdata(addr, mlen) << 8;
-		else
-		    sum += in_cksumdata(addr, mlen);
-
-		clen += mlen;
-		len -= mlen;
-	}
+	len -= skip;
+
+	a.csum = 0;
+	a.clen = 0;
+	m_apply(m, skip, len, in_cksum_cb, &a);
+	sum = a.csum;
 	REDUCE16;
 	return (~sum & 0xffff);
 }