diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index b29061247d00..7cff0a7d9251 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -1561,7 +1561,7 @@ m_uiotombuf(struct uio *uio, int how, int len, int align, int flags)
  * Copy an mbuf chain into a uio limited by len if set.
  */
 int
-m_mbuftouio(struct uio *uio, struct mbuf *m, int len)
+m_mbuftouio(struct uio *uio, const struct mbuf *m, int len)
 {
 	int error, length, total;
 	int progress = 0;
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 1651767687d8..ecc5c2a9aab2 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -614,7 +614,7 @@ struct mbuf	*m_getjcl(int, short, int, int);
 struct mbuf	*m_getm2(struct mbuf *, int, int, short, int);
 struct mbuf	*m_getptr(struct mbuf *, int, int *);
 u_int		 m_length(struct mbuf *, struct mbuf **);
-int		 m_mbuftouio(struct uio *, struct mbuf *, int);
+int		 m_mbuftouio(struct uio *, const struct mbuf *, int);
 void		 m_move_pkthdr(struct mbuf *, struct mbuf *);
 int		 m_pkthdr_init(struct mbuf *, int);
 struct mbuf	*m_prepend(struct mbuf *, int, int);