Index: mbuf.h
===================================================================
--- mbuf.h	(revision 209649)
+++ mbuf.h	(working copy)
@@ -511,7 +511,10 @@
 static __inline struct mbuf *
 m_free(struct mbuf *m)
 {
-	struct mbuf *n = m->m_next;
+	struct mbuf *n;
+	if (!m)
+		return (NULL);
+	*n = m->m_next;
 
 	if (m->m_flags & M_EXT)
 		mb_free_ext(m);