diff --git a/src/unix/lwt_bytes.ml b/src/unix/lwt_bytes.ml
index b3cc1a7550..b1936952a9 100644
--- a/src/unix/lwt_bytes.ml
+++ b/src/unix/lwt_bytes.ml
@@ -5,8 +5,6 @@
 
 open Bigarray
 
-open Lwt.Infix
-
 type t = (char, int8_unsigned_elt, c_layout) Array1.t
 
 let create size = Array1.create char c_layout size
@@ -101,33 +99,11 @@ let copy buf =
 
 open Lwt_unix
 
-external stub_read : Unix.file_descr -> t -> int -> int -> int = "lwt_unix_bytes_read"
-external read_job : Unix.file_descr -> t -> int -> int -> int job = "lwt_unix_bytes_read_job"
-
-let read fd buf pos len =
-  if pos < 0 || len < 0 || pos > length buf - len then
-    invalid_arg "Lwt_bytes.read"
-  else
-    blocking fd >>= function
-    | true ->
-      wait_read fd >>= fun () ->
-      run_job (read_job (unix_file_descr fd) buf pos len)
-    | false ->
-      wrap_syscall Read fd (fun () -> stub_read (unix_file_descr fd) buf pos len)
+let read =
+  Lwt_unix.read_bigarray "Lwt_bytes.read" [@ocaml.warning "-3"]
 
-external stub_write : Unix.file_descr -> t -> int -> int -> int = "lwt_unix_bytes_write"
-external write_job : Unix.file_descr -> t -> int -> int -> int job = "lwt_unix_bytes_write_job"
-
-let write fd buf pos len =
-  if pos < 0 || len < 0 || pos > length buf - len then
-    invalid_arg "Lwt_bytes.write"
-  else
-    blocking fd >>= function
-    | true ->
-      wait_write fd >>= fun () ->
-      run_job (write_job (unix_file_descr fd) buf pos len)
-    | false ->
-      wrap_syscall Write fd (fun () -> stub_write (unix_file_descr fd) buf pos len)
+let write =
+  Lwt_unix.write_bigarray "Lwt_bytes.write" [@ocaml.warning "-3"]
 
 external stub_recv : Unix.file_descr -> t -> int -> int -> Unix.msg_flag list -> int = "lwt_unix_bytes_recv"
 
diff --git a/src/unix/lwt_unix.cppo.ml b/src/unix/lwt_unix.cppo.ml
index 341cb5efda..0863d37124 100644
--- a/src/unix/lwt_unix.cppo.ml
+++ b/src/unix/lwt_unix.cppo.ml
@@ -617,6 +617,9 @@ let close ch =
   else
     run_job (close_job ch.fd)
 
+type bigarray =
+  (char, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t
+
 let wait_read ch =
   Lwt.catch
     (fun () ->
@@ -640,6 +643,24 @@ let read ch buf pos len =
     | false ->
       wrap_syscall Read ch (fun () -> stub_read ch.fd buf pos len)
 
+external stub_read_bigarray :
+  Unix.file_descr -> bigarray -> int -> int -> int = "lwt_unix_bytes_read"
+external read_bigarray_job :
+  Unix.file_descr -> bigarray -> int -> int -> int job =
+  "lwt_unix_bytes_read_job"
+
+let read_bigarray function_name fd buf pos len =
+  if pos < 0 || len < 0 || pos > Bigarray.Array1.dim buf - len then
+    invalid_arg function_name
+  else
+    blocking fd >>= function
+    | true ->
+      wait_read fd >>= fun () ->
+      run_job (read_bigarray_job (unix_file_descr fd) buf pos len)
+    | false ->
+      wrap_syscall Read fd (fun () ->
+        stub_read_bigarray (unix_file_descr fd) buf pos len)
+
 let wait_write ch =
   Lwt.catch
     (fun () ->
@@ -667,10 +688,27 @@ let write_string ch buf pos len =
   let buf = Bytes.unsafe_of_string buf in
   write ch buf pos len
 
+external stub_write_bigarray :
+  Unix.file_descr -> bigarray -> int -> int -> int = "lwt_unix_bytes_write"
+external write_bigarray_job :
+  Unix.file_descr -> bigarray -> int -> int -> int job =
+  "lwt_unix_bytes_write_job"
+
+let write_bigarray function_name fd buf pos len =
+  if pos < 0 || len < 0 || pos > Bigarray.Array1.dim buf - len then
+    invalid_arg function_name
+  else
+    blocking fd >>= function
+    | true ->
+      wait_write fd >>= fun () ->
+      run_job (write_bigarray_job (unix_file_descr fd) buf pos len)
+    | false ->
+      wrap_syscall Write fd (fun () ->
+        stub_write_bigarray (unix_file_descr fd) buf pos len)
+
 module IO_vectors =
 struct
-  type _bigarray =
-    (char, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t
+  type _bigarray = bigarray
 
   type buffer =
     | Bytes of bytes
@@ -780,13 +818,25 @@ external readv_job : Unix.file_descr -> IO_vectors.t -> int -> int job =
 let readv fd io_vectors =
   let count = check_io_vectors "Lwt_unix.readv" io_vectors in
 
-  Lazy.force fd.blocking >>= function
-  | true ->
-    wait_read fd >>= fun () ->
-    run_job (readv_job fd.fd io_vectors count)
-  | false ->
-    wrap_syscall Read fd (fun () ->
-      stub_readv fd.fd io_vectors.IO_vectors.prefix count)
+  if Sys.win32 then
+    match io_vectors.IO_vectors.prefix with
+    | [] ->
+      Lwt.return 0
+    | first::_ ->
+      match first.buffer with
+      | Bytes buffer ->
+        read fd buffer first.offset first.length
+      | Bigarray buffer ->
+        read_bigarray "Lwt_unix.readv" fd buffer first.offset first.length
+
+  else
+    Lazy.force fd.blocking >>= function
+    | true ->
+      wait_read fd >>= fun () ->
+      run_job (readv_job fd.fd io_vectors count)
+    | false ->
+      wrap_syscall Read fd (fun () ->
+        stub_readv fd.fd io_vectors.IO_vectors.prefix count)
 
 external stub_writev :
   Unix.file_descr -> IO_vectors.io_vector list -> int -> int =
@@ -798,13 +848,25 @@ external writev_job : Unix.file_descr -> IO_vectors.t -> int -> int job =
 let writev fd io_vectors =
   let count = check_io_vectors "Lwt_unix.writev" io_vectors in
 
-  Lazy.force fd.blocking >>= function
-  | true ->
-    wait_write fd >>= fun () ->
-    run_job (writev_job fd.fd io_vectors count)
-  | false ->
-    wrap_syscall Write fd (fun () ->
-      stub_writev fd.fd io_vectors.IO_vectors.prefix count)
+  if Sys.win32 then
+    match io_vectors.IO_vectors.prefix with
+    | [] ->
+      Lwt.return 0
+    | first::_ ->
+      match first.buffer with
+      | Bytes buffer ->
+        write fd buffer first.offset first.length
+      | Bigarray buffer ->
+        write_bigarray "Lwt_unix.writev" fd buffer first.offset first.length
+
+  else
+    Lazy.force fd.blocking >>= function
+    | true ->
+      wait_write fd >>= fun () ->
+      run_job (writev_job fd.fd io_vectors count)
+    | false ->
+      wrap_syscall Write fd (fun () ->
+        stub_writev fd.fd io_vectors.IO_vectors.prefix count)
 
 (* +-----------------------------------------------------------------+
    | Seeking and truncating                                          |
diff --git a/src/unix/lwt_unix.cppo.mli b/src/unix/lwt_unix.cppo.mli
index 54e8f26add..ee7f1f54b7 100644
--- a/src/unix/lwt_unix.cppo.mli
+++ b/src/unix/lwt_unix.cppo.mli
@@ -1541,3 +1541,11 @@ val somaxconn : unit -> int
 
 val retained : 'a -> bool ref
   (** @deprecated Used for testing. *)
+
+val read_bigarray :
+  string -> file_descr -> IO_vectors._bigarray -> int -> int -> int Lwt.t
+  [@@ocaml.deprecated " This is an internal function."]
+
+val write_bigarray :
+  string -> file_descr -> IO_vectors._bigarray -> int -> int -> int Lwt.t
+  [@@ocaml.deprecated " This is an internal function."]
diff --git a/test/unix/test_lwt_unix.cppo.ml b/test/unix/test_lwt_unix.cppo.ml
index 5fbec41337..3217a836a6 100644
--- a/test/unix/test_lwt_unix.cppo.ml
+++ b/test/unix/test_lwt_unix.cppo.ml
@@ -378,13 +378,22 @@ let readv_tests =
     Lwt.return (bytes_written = Bytes.length data)
   in
 
-  let reader read_fd io_vectors underlying expected_count expected_data =
+  let reader
+      ?(close = true)
+      read_fd
+      io_vectors
+      underlying
+      expected_count
+      expected_data =
       fun () ->
     Gc.full_major ();
     let t = Lwt_unix.readv read_fd io_vectors in
     Gc.full_major ();
     t >>= fun bytes_read ->
-    Lwt_unix.close read_fd >>= fun () ->
+    (if close then
+      Lwt_unix.close read_fd
+    else
+      Lwt.return ()) >>= fun () ->
 
     let actual =
       List.fold_left (fun acc -> function
@@ -497,6 +506,24 @@ let readv_tests =
         Lwt_list.for_all_s (fun t -> t ())
           [writer write_fd (expected ^ "a");
            reader read_fd io_vectors underlying limit (expected ^ "_")]);
+
+    test "readv: windows" ~only_if:(fun () -> Sys.win32) begin fun () ->
+      let read_fd, write_fd = Lwt_unix.pipe () in
+
+      let io_vectors, underlying =
+        make_io_vectors [
+          `Bytes (1, 3, 1);
+          `Bigarray (1, 4, 1)
+        ]
+      in
+
+      Lwt_list.for_all_s (fun t -> t ()) [
+        writer write_fd "foobar";
+        reader ~close:false read_fd io_vectors underlying 3 "_foo_______";
+        (fun () -> Lwt_unix.IO_vectors.drop io_vectors 3; Lwt.return true);
+        reader read_fd io_vectors underlying 3 "_foo__bar__";
+      ]
+    end;
   ]
 
 let writev_tests =
@@ -512,13 +539,17 @@ let writev_tests =
     io_vectors
   in
 
-  let writer ?blocking write_fd io_vectors data_length = fun () ->
+  let writer ?(close = true) ?blocking write_fd io_vectors data_length =
+      fun () ->
     Lwt_unix.blocking write_fd >>= fun is_blocking ->
     Gc.full_major ();
     let t = Lwt_unix.writev write_fd io_vectors in
     Gc.full_major ();
     t >>= fun bytes_written ->
-    Lwt_unix.close write_fd >>= fun () ->
+    (if close then
+      Lwt_unix.close write_fd
+    else
+      Lwt.return ()) >>= fun () ->
     let blocking_matches =
       match blocking, is_blocking with
       | Some v, v' when v <> v' ->
@@ -743,6 +774,24 @@ let writev_tests =
         Lwt.return
           (io_correct &&
            not (Lwt_unix.IO_vectors.is_empty io_vectors)));
+
+    test "writev: windows" ~only_if:(fun () -> Sys.win32) begin fun () ->
+      let io_vectors =
+        make_io_vectors [
+          `Bytes ("foo", 0, 3);
+          `Bigarray ("bar", 0, 3);
+        ]
+      in
+
+      let read_fd, write_fd = Lwt_unix.pipe () in
+
+      Lwt_list.for_all_s (fun t -> t ()) [
+        writer ~close:false write_fd io_vectors 3;
+        (fun () -> Lwt_unix.IO_vectors.drop io_vectors 3; Lwt.return true);
+        writer write_fd io_vectors 3;
+        reader read_fd "foobar";
+      ]
+    end;
   ]
 
 let send_recv_msg_tests = [