diff --git a/src/core/meta_map.ourown.ml b/src/core/meta_map.ourown.ml
index 09260b5..ae3aa65 100644
--- a/src/core/meta_map.ourown.ml
+++ b/src/core/meta_map.ourown.ml
@@ -48,14 +48,14 @@ module M = Map.Make (struct
   let compare (i : int) j = Stdlib.compare i j
 end)
 
-type t = exn_pair M.t
+type t = { m: exn_pair M.t } [@@unboxed]
 
 let empty = M.empty
-let[@inline] mem k (self : t) = M.mem (Key.id k) self
+let[@inline] mem k (self : t) = M.mem (Key.id k) self.m
 
 let find_exn (type a) (k : a Key.t) (self : t) : a =
   let module K = (val k) in
-  let (E_pair (_, e)) = M.find K.id self in
+  let (E_pair (_, e)) = M.find K.id self.m in
   match e with
   | K.Store v -> v
   | _ -> assert false
@@ -63,14 +63,14 @@ let find_exn (type a) (k : a Key.t) (self : t) : a =
 let find k (self : t) = try Some (find_exn k self) with Not_found -> None
 
 open struct
-  let add_e_pair_ p t =
+  let add_e_pair_ p self =
     let (E_pair ((module K), _)) = p in
-    M.add K.id p t
+    { m = M.add K.id p self.m }
 
   let add_pair_ p (self : t) : t =
     let (B (((module K) as k), v)) = p in
     let p = E_pair (k, K.Store v) in
-    M.add K.id p self
+    { m = M.add K.id p self.m }
 end
 
 let add (type a) (k : a Key.t) v (self : t) : t =
@@ -79,13 +79,13 @@ let add (type a) (k : a Key.t) v (self : t) : t =
 
 let remove (type a) (k : a Key.t) (self : t) : t =
   let module K = (val k) in
-  M.remove K.id self
+  { m = M.remove K.id self.m }
 
-let cardinal : t -> int = M.cardinal
+let[@inline] cardinal (self : t) = M.cardinal self.m
 let length = cardinal
-let iter f (self : t) = M.iter (fun _ p -> f (pair_of_e_pair p)) self
+let iter f (self : t) = M.iter (fun _ p -> f (pair_of_e_pair p)) self.m
 
 let to_list (self : t) : binding list =
-  M.fold (fun _ p l -> pair_of_e_pair p :: l) self []
+  M.fold (fun _ p l -> pair_of_e_pair p :: l) self.m []
 
 let add_list (self : t) l = List.fold_right add_pair_ l self