diff --git a/runtime/wasm/runtime.js b/runtime/wasm/runtime.js
index 317d7b968f..f3d649ccd5 100644
--- a/runtime/wasm/runtime.js
+++ b/runtime/wasm/runtime.js
@@ -397,6 +397,12 @@
     channel_list,
     exit: (n) => isNode && process.exit(n),
     argv: () => (isNode ? process.argv.slice(1) : ["a.out"]),
+    ostype: () =>
+    globalThis.process &&
+    globalThis.process.platform &&
+    globalThis.process.platform === "win32"
+      ? "Win32"
+      : "Unix",
     getenv: (n) => (isNode ? process.env[n] : null),
     system: (c) => {
       var res = require("node:child_process").spawnSync(c, {
diff --git a/runtime/wasm/sys.wat b/runtime/wasm/sys.wat
index b397c89a82..de0f8ca50b 100644
--- a/runtime/wasm/sys.wat
+++ b/runtime/wasm/sys.wat
@@ -36,6 +36,7 @@
       (func $caml_raise_sys_error (param (ref eq))))
    (import "fail" "caml_raise_not_found" (func $caml_raise_not_found))
    (import "bindings" "argv" (func $argv (result (ref extern))))
+   (import "bindings" "ostype" (func $ostype (result anyref)))
    (import "bindings" "system" (func $system (param anyref) (result (ref eq))))
    (import "bindings" "getenv" (func $getenv (param anyref) (result anyref)))
    (import "bindings" "time" (func $time (result f64)))
@@ -136,26 +137,27 @@
    (func (export "caml_sys_const_ostype_unix")
       (param (ref eq)) (result (ref eq))
       ;; ZZZ
-      (ref.i31 (i32.const 1)))
+      (ref.i31 (i32.const 0)))
 
    (func (export "caml_sys_const_ostype_win32")
       (param (ref eq)) (result (ref eq))
       ;; ZZZ
-      (ref.i31 (i32.const 0)))
+      (ref.i31 (i32.const 1)))
 
    (func (export "caml_sys_const_ostype_cygwin")
       (param (ref eq)) (result (ref eq))
       ;; ZZZ
       (ref.i31 (i32.const 0)))
 
-   (data $Unix "Unix")
+   (func $get_os_type (result (ref eq))
+      (return_call $caml_string_of_jsstring (call $wrap (call $ostype))))
 
    (func (export "caml_sys_get_config")
       (param (ref eq)) (result (ref eq))
       ;; ZZZ
       ;; (call $log_js (string.const "caml_sys_get_config"))
       (array.new_fixed $block 4 (ref.i31 (i32.const 0))
-         (array.new_data $string $Unix (i32.const 0) (i32.const 4))
+         (call $get_os_type)
          (ref.i31 (i32.const 32))
          (ref.i31 (i32.const 0))))
 
diff --git a/runtime/wasm/unix.wat b/runtime/wasm/unix.wat
index 797a3b3f3f..4740b129ee 100644
--- a/runtime/wasm/unix.wat
+++ b/runtime/wasm/unix.wat
@@ -99,4 +99,11 @@
    (func $unix_inet_addr_of_string (export "unix_inet_addr_of_string")
       (param (ref eq)) (result (ref eq))
       (ref.i31 (i32.const 0)))
+   (export "caml_unix_filedescr_of_fd" (func $unix_filedescr_of_fd))
+   (func $unix_filedescr_of_fd (export "unix_filedescr_of_fd")
+      (param (ref eq)) (result (ref eq))
+      (local.get 0))
+   (func $unix_cleanup (export "caml_unix_cleanup")
+      (param (ref eq)) (result (ref eq))
+      (ref.i31 (i32.const 0)))
 )