diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index 6d66245c5bce..009b812b0bcf 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -714,13 +714,26 @@ m_print(const struct mbuf *m)
 int
 m_fixhdr(struct mbuf *m0)
 {
-	struct mbuf *m = m0;
-	int len = 0;
+	int len;
 
-	while (m) {
-		len += m->m_len;
-		m = m->m_next;
-	}
+	len = m_length(m0, NULL);
 	m0->m_pkthdr.len = len;
-	return len;
+	return (len);
+}
+
+int
+m_length(struct mbuf *m0, struct mbuf **last)
+{
+	struct mbuf *m;
+	int len;
+
+	len = 0;
+	for (m = m0; m != NULL; m = m->m_next) {
+		len += m->m_len;
+		if (m->m_next == NULL)
+			break;
+	}
+	if (last != NULL)
+		*last = m;
+	return (len);
 }
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index a791d356a804..b4bd624a29d9 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -489,6 +489,7 @@ struct	mbuf	*m_getcl(int, short, int);
 struct	mbuf	*m_gethdr(int, short);
 struct	mbuf	*m_gethdr_clrd(int, short);
 struct	mbuf	*m_getm(struct mbuf *, int, int, short);
+int		 m_length(struct mbuf *m, struct mbuf **l);
 struct	mbuf	*m_prepend(struct mbuf *, int, int);
 void		 m_print(const struct mbuf *m);
 struct	mbuf	*m_pulldown(struct mbuf *, int, int, int *);