diff --git a/src/resource.ml b/src/resource.ml
new file mode 100644
index 0000000..fed5e93
--- /dev/null
+++ b/src/resource.ml
@@ -0,0 +1,9 @@
+type 'a t = ([> `Mem_fd ] as 'a) Eio.Resource.t
+
+type ('t, _, _) Eio.Resource.pi +=
+  | T : ('t, 't -> Low_level.Fd.t, [> `Mem_fd ]) Eio.Resource.pi
+
+let fd (Eio.Resource.T (t, ops)) = Eio.Resource.get ops T t
+
+let fd_opt (Eio.Resource.T (t, ops)) =
+  match Eio.Resource.get_opt ops T with Some f -> Some (f t) | None -> None