diff --git a/src/lib/eunix.ml b/src/lib/eunix.ml
index c803b6f..1aa63e0 100644
--- a/src/lib/eunix.ml
+++ b/src/lib/eunix.ml
@@ -32,16 +32,14 @@ let get_user_and_host fs =
 
 external getpgrp : unit -> int = "caml_merry_getpgrp"
 external tcgetpgrp : Unix.file_descr -> int = "caml_merry_tcgetpgrp"
-external tcsetpgrp : int -> int -> int = "caml_merry_tcsetpgrp"
+external tcsetpgrp : Unix.file_descr -> int -> int = "caml_merry_tcsetpgrp"
 
 let delegate_control ~pgid fn =
-  let shell_pid = Unix.getpid () in
+  let shell_pid = getpgrp () in
   Fun.protect
-    ~finally:(fun () ->
-      let _ : int = tcsetpgrp 0 shell_pid in
-      ())
+    ~finally:(fun () -> assert (Int.equal 0 @@ tcsetpgrp Unix.stdin shell_pid))
     (fun () ->
-      match tcsetpgrp (Obj.magic Unix.stdin : int) pgid with
+      match tcsetpgrp Unix.stdin pgid with
       | 0 -> fn ()
       | n -> Fmt.failwith "tcsetpgrp: %i" n)