--- src/ftp.ml.orig
+++ src/ftp.ml
@@ -275,7 +275,7 @@
   let flags = if append then [O_WRONLY; O_APPEND] else [O_WRONLY; O_TRUNC; O_CREAT] in
   let foutd = openfile fout flags 0o644 in
   let buf_len = 16384 in
-  let buf = String.create buf_len in
+  let buf = Bytes.create buf_len in
   let len = ref 1 in
   let r = send_command fc (Retrieve fin) in
     if (fst r) = 550 then raise Not_found;
@@ -473,7 +473,7 @@

   val close : file_descr -> unit

-  val read : file_descr -> string -> int -> int -> int
+  val read : file_descr -> bytes -> int -> int -> int

   type seek_command =
     | SEEK_SET
--- src/ftp.mli.orig
+++ src/ftp.mli
@@ -94,7 +94,7 @@
 val resume_file : ftp_connection -> string -> string -> int -> unit

 (** [get_file_portion fc src file_ofs buf ofs len] downloads [len] octets of file [src] starting at position [file_ofs] and stores it in [buf] starting at position [ofs]. Returns the number of bytes actually read. *)
-val get_file_portion : ftp_connection -> string -> int -> string -> int -> int -> int
+val get_file_portion : ftp_connection -> string -> int -> bytes -> int -> int -> int

 (** [mv fc src dst] moves the file [src] to [dst]. *)
 val mv : ftp_connection -> string -> string -> unit
@@ -133,7 +133,7 @@
   val close : file_descr -> unit

   (** Read data in an opened file. *)
-  val read : file_descr -> string -> int -> int -> int
+  val read : file_descr -> bytes -> int -> int -> int

   (** Positioning modes for [lseek]. *)
   type seek_command =