diff -ur lwt-2.5.0.old/src/ssl/lwt_ssl.mli lwt-2.5.0/src/ssl/lwt_ssl.mli
--- lwt-2.5.0.old/src/ssl/lwt_ssl.mli	2015-07-03 13:39:30.000000000 +0100
+++ lwt-2.5.0/src/ssl/lwt_ssl.mli	2017-11-17 16:07:20.829197330 +0000
@@ -56,8 +56,8 @@
 val ssl_accept_handshake  : uninitialized_socket -> socket Lwt.t
 (** Await a SSL/TLS handshake on the specified socket (used by servers). *)
 
-val read : socket -> string -> int -> int -> int Lwt.t
-val write : socket -> string -> int -> int -> int Lwt.t
+val read : socket -> bytes -> int -> int -> int Lwt.t
+val write : socket -> bytes -> int -> int -> int Lwt.t
 
 val read_bytes : socket -> Lwt_bytes.t -> int -> int -> int Lwt.t
 val write_bytes : socket -> Lwt_bytes.t -> int -> int -> int Lwt.t