diff --git a/src/unix/lwt_process_stubs.c b/src/unix/lwt_process_stubs.c
index 629682bac..fea5e032b 100644
--- a/src/unix/lwt_process_stubs.c
+++ b/src/unix/lwt_process_stubs.c
@@ -9,8 +9,20 @@
 
 #include "lwt_unix.h"
 
-#if OCAML_VERSION < 41300
+/* needed for caml_stat_strdup_to_os before ocaml 4.13, and for
+   caml_win32_multi_byte_to_wide_char, at least as of ocaml 5.0 */
 #define CAML_INTERNALS
+#if OCAML_VERSION < 50000
+#define caml_win32_multi_byte_to_wide_char win_multi_byte_to_wide_char
+#endif
+#if OCAML_VERSION = 52000
+/* see https://github.com/ocsigen/lwt/pull/967#issuecomment-2273495094
+ * TL;DR: some OCaml upstream issue means this extern is not included on the
+ * windows, it's added explicitly here instead. */
+CAMLextern int caml_win32_multi_byte_to_wide_char(const char* s,
+                                                  int slen,
+                                                  wchar_t *out,
+                                                  int outlen);
 #endif
 
 #include <caml/alloc.h>
@@ -68,6 +80,7 @@ CAMLprim value lwt_process_create_process(value prog, value cmdline, value env,
   HANDLE hp, fd0, fd1, fd2;
   HANDLE to_close0 = INVALID_HANDLE_VALUE, to_close1 = INVALID_HANDLE_VALUE,
     to_close2 = INVALID_HANDLE_VALUE;
+  int size;
 
   fd0 = get_handle(Field(fds, 0));
   fd1 = get_handle(Field(fds, 1));
@@ -94,11 +107,24 @@ CAMLprim value lwt_process_create_process(value prog, value cmdline, value env,
   char_os
     *progs = string_option(prog),
     *cmdlines = caml_stat_strdup_to_os(String_val(cmdline)),
-    *envs = string_option(env),
     *cwds = string_option(cwd);
 
 #undef string_option
 
+  char_os *envs;
+  if (Is_some(env)) {
+    env = Some_val(env);
+    size =
+      caml_win32_multi_byte_to_wide_char(String_val(env),
+                                         caml_string_length(env), NULL, 0);
+    envs = caml_stat_alloc((size + 1)*sizeof(char_os));
+    caml_win32_multi_byte_to_wide_char(String_val(env),
+                                       caml_string_length(env), envs, size);
+    envs[size] = 0;
+  } else {
+    envs = NULL;
+  }
+
   flags |= CREATE_UNICODE_ENVIRONMENT;
   if (! CreateProcess(progs, cmdlines, NULL, NULL, TRUE, flags,
                       envs, cwds, &si, &pi)) {
diff --git a/test/unix/dummy.ml b/test/unix/dummy.ml
index 2ec9f2577..f650450ac 100644
--- a/test/unix/dummy.ml
+++ b/test/unix/dummy.ml
@@ -23,9 +23,18 @@ let read () =
 let write fd =
   assert (test_input_len = Unix.write fd test_input 0 test_input_len)
 
+let printenv () =
+  (* stdout is in text mode by default, which converts \n to \r\n on Windows.
+    switch to binary mode to prevent this, so the output is the same across
+    platforms. *)
+  set_binary_mode_out stdout true;
+  Array.iter (Printf.printf "%s\n") (Unix.unsafe_environment ());
+  flush stdout
+
 let () =
   match Sys.argv.(1) with
   | "read" -> exit @@ if read () then 0 else 1
   | "write" -> write Unix.stdout
   | "errwrite" -> write Unix.stderr
+  | "printenv" -> printenv ()
   | _ -> invalid_arg "Sys.argv"
diff --git a/test/unix/test_lwt_process.ml b/test/unix/test_lwt_process.ml
index cad23768b..7404f336d 100644
--- a/test/unix/test_lwt_process.ml
+++ b/test/unix/test_lwt_process.ml
@@ -8,7 +8,6 @@ open Lwt.Infix
 
 let expected_str = "the quick brown fox jumps over the lazy dog"
 let expected = Bytes.of_string expected_str
-let expected_len = Bytes.length expected
 
 let check_status ?(status=(=) 0) = function
   | Unix.WEXITED n when status n -> Lwt.return_true
@@ -22,7 +21,8 @@ let check_status ?(status=(=) 0) = function
     Printf.eprintf "stopped with signal %d" x;
     Lwt.return_false
 
-let pwrite ~stdin pout =
+let pwrite ~stdin pout expected =
+  let expected_len = Bytes.length expected in
   let args = [|"dummy.exe"; "read"|] in
   let proc = Lwt_process.exec ~stdin ("./dummy.exe", args) in
   let write = Lwt.finalize
@@ -33,26 +33,47 @@ let pwrite ~stdin pout =
   assert (n = expected_len);
   check_status r
 
-let pread ?stdout ?stderr pin =
-  let buf = Bytes.create expected_len in
-  let proc = match stdout, stderr with
-    | Some stdout, None ->
-       let args = [|"dummy.exe"; "write"|] in
-       Lwt_process.exec ~stdout ("./dummy.exe", args)
-    | None, Some stderr ->
-       let args = [|"dummy.exe"; "errwrite"|] in
-       Lwt_process.exec ~stderr ("./dummy.exe", args)
-    | _ -> assert false
+let read_all ic buf ofs len =
+  let rec loop ic buf ofs len =
+    Lwt_unix.read ic buf ofs len >>= function
+    | 0 ->
+        Lwt.return ofs
+    | n ->
+        let ofs = ofs + n in
+        let len = len - n in
+        if len = 0 then
+          Lwt.return ofs
+        else
+          loop ic buf ofs len
   in
-  let read = Lwt_unix.read pin buf 0 expected_len in
+  loop ic buf ofs len
+
+let pread ?env ?stdout ?stderr pin cmd expected =
+  (match stdout, stderr with
+    | Some _, None
+    | None, Some _ ->
+      ()
+    | _ -> assert false);
+  let expected_len = Bytes.length expected in
+  let buf = Bytes.create expected_len in
+  let args = [|"dummy.exe"; cmd|] in
+  let proc = Lwt_process.exec ?env ?stdout ?stderr ("./dummy.exe", args) in
+  let read = read_all pin buf 0 expected_len in
   proc >>= fun r ->
   read >>= fun n ->
-  assert (n = expected_len);
+  (if n <> expected_len then Printf.ksprintf failwith "expected %d bytes, got %d" expected_len n);
   assert (Bytes.equal buf expected);
   Lwt_unix.read pin buf 0 1 >>= fun n ->
-  assert (n = 0);
+  if n <> 0 then Printf.ksprintf failwith "expected 0 bytes remaining, got %d" n;
   check_status r
 
+let bytes_of_env env =
+  env
+  |> Array.map (Printf.sprintf "%s\n")
+  |> Array.to_list
+  |> String.concat ""
+  |> Bytes.of_string
+
 let suite = suite "lwt_process" [
   (* The sleep command is not available on Win32. *)
   test "lazy_undefined" ~only_if:(fun () -> not Sys.win32)
@@ -93,15 +114,36 @@ let suite = suite "lwt_process" [
   test "can write to subproc stdin"
     (fun () ->
       let pin, pout = Lwt_unix.pipe_out ~cloexec:true () in
-      pwrite ~stdin:(`FD_move pin) pout);
+      pwrite ~stdin:(`FD_move pin) pout expected);
 
   test "can read from subproc stdout"
     (fun () ->
       let pin, pout = Lwt_unix.pipe_in ~cloexec:true () in
-      pread ~stdout:(`FD_move pout) pin);
+      pread ~stdout:(`FD_move pout) pin "write" expected);
 
   test "can read from subproc stderr"
     (fun () ->
       let pin, perr = Lwt_unix.pipe_in ~cloexec:true () in
-      pread ~stderr:(`FD_move perr) pin);
+      pread ~stderr:(`FD_move perr) pin "errwrite" expected);
+
+  test "overrides env"
+    (fun () ->
+      let env = [| "FOO=1" |] in
+      let expected = Bytes.of_string "FOO=1\n" in
+      let pin, pout = Lwt_unix.pipe_in ~cloexec:true () in
+      pread ~env ~stdout:(`FD_move pout) pin "printenv" expected);
+
+  test "passes env"
+    (fun () ->
+      let env = Unix.unsafe_environment () in
+      let expected = bytes_of_env env in
+      let pin, pout = Lwt_unix.pipe_in ~cloexec:true () in
+      pread ~env ~stdout:(`FD_move pout) pin "printenv" expected);
+
+  test "inherits env"
+    (fun () ->
+      let env = Unix.unsafe_environment () in
+      let expected = bytes_of_env env in
+      let pin, pout = Lwt_unix.pipe_in ~cloexec:true () in
+      pread ?env:None ~stdout:(`FD_move pout) pin "printenv" expected);
 ]