diff --git a/engine/lib/local_ident.mli b/engine/lib/local_ident.mli
index 2ad0db981..e2e2d5d4e 100644
--- a/engine/lib/local_ident.mli
+++ b/engine/lib/local_ident.mli
@@ -9,7 +9,7 @@ module T : sig
     | SideEffectHoistVar  (** A variable generated by `Side_effect_utils` *)
   [@@deriving show, yojson, hash, compare, sexp, eq]
 
-  type id [@@deriving show, yojson, hash, compare, sexp, eq]
+  type id = kind * int [@@deriving show, yojson, hash, compare, sexp, eq]
 
   val mk_id : kind -> int -> id