diff --git a/lib/async/release_async.ml b/lib/async/release_async.ml
index 6c1bff7..7b3294e 100644
--- a/lib/async/release_async.ml
+++ b/lib/async/release_async.ml
@@ -243,6 +243,9 @@ struct
       | Ok () -> Std_unix.WEXITED 0
       | Error (`Exit_non_zero s) -> Std_unix.WEXITED s
       | Error (`Signal s) -> Std_unix.WSIGNALED (Signal.to_caml_int s)
+
+    let wrap_file_descr fd =
+      Fd.create (Fd.Kind.Socket `Active) fd (Info.of_string "<wrap_file_descr>")
   end
 
   module Bytes = struct
diff --git a/lib/core/release_future.mli b/lib/core/release_future.mli
index 40bad9d..2979931 100644
--- a/lib/core/release_future.mli
+++ b/lib/core/release_future.mli
@@ -92,6 +92,7 @@ module type S = sig
     val unix_socket_of_fd : fd -> ('state, unix) socket
     val unlink : string -> unit future
     val waitpid : int -> Unix.process_status future
+    val wrap_file_descr : Unix.file_descr -> fd
   end
 
   module Bytes : sig
diff --git a/lib/lwt/release_lwt.ml b/lib/lwt/release_lwt.ml
index f2f28d7..bc615e4 100644
--- a/lib/lwt/release_lwt.ml
+++ b/lib/lwt/release_lwt.ml
@@ -138,6 +138,8 @@ struct
     let unlink = Lwt_unix.unlink
     let waitpid pid =
       Lwt_unix.waitpid [] pid >>= fun (_, status) -> return status
+    let wrap_file_descr fd =
+      Lwt_unix.of_unix_file_descr fd
   end
 
   module Bytes = struct