diff --git a/src/lib/uTop_main.cppo.ml b/src/lib/uTop_main.cppo.ml
index f613ea7..493e6c9 100644
--- a/src/lib/uTop_main.cppo.ml
+++ b/src/lib/uTop_main.cppo.ml
@@ -399,6 +399,8 @@ let with_loc loc str = {
 
 (* A rule for rewriting a toplevel expression. *)
 type rewrite_rule = {
+  type_to_rewrite : Longident.t;
+  mutable path_to_rewrite : Path.t option;
   required_values : Longident.t list;
   (* Values that must exist and be persistent for the rule to apply. *)
   rewrite : Location.t -> Parsetree.expression -> Parsetree.expression;
@@ -407,10 +409,6 @@ type rewrite_rule = {
   (* Whether the rule is enabled or not. *)
 }
 
-(* Rewrite rules, indexed by the identifier of the type
-   constructor. *)
-let rewrite_rules : (Longident.t, rewrite_rule) Hashtbl.t = Hashtbl.create 42
-
 let longident_lwt_main_run = Longident.Ldot (Longident.Lident "Lwt_main", "run")
 let longident_async_thread_safe_block_on_async_exn =
   Longident.parse "Async.Std.Thread_safe.block_on_async_exn"
@@ -436,9 +434,11 @@ let nolabel = Asttypes.Nolabel
 let nolabel = ""
 #endif
 
-let () =
+let rewrite_rules = [
   (* Rewrite Lwt.t expressions to Lwt_main.run <expr> *)
-  Hashtbl.add rewrite_rules (Longident.Ldot (Longident.Lident "Lwt", "t")) {
+  {
+    type_to_rewrite = Longident.parse "Lwt.t";
+    path_to_rewrite = None;
     required_values = [longident_lwt_main_run];
     rewrite = (fun loc e ->
 #if OCAML_VERSION < (4, 02, 0)
@@ -460,7 +460,9 @@ let () =
 
   (* Rewrite Async.Std.Defered.t expressions to
      Async.Std.Thread_safe.block_on_async_exn (fun () -> <expr>). *)
-  let rule = {
+  {
+    type_to_rewrite = Longident.parse "Async.Std.Deferred.t";
+    path_to_rewrite = None;
     required_values = [longident_async_thread_safe_block_on_async_exn];
     rewrite = (fun loc e ->
 #if OCAML_VERSION < (4, 02, 0)
@@ -482,21 +484,32 @@ let () =
 #endif
     );
     enabled = UTop.auto_run_async;
-  } in
-  let deferred_aliases =
-    [ "Async_core.Ivar.Deferred.t"
-    ; "Async_kernel.Ivar.Deferred.t"
-    ; "Async_kernel.Deferred0.t"
-    ]
-  in
-  List.iter (fun s ->
-    Hashtbl.add rewrite_rules (Longident.parse s) rule)
-    deferred_aliases
+  }
+]
 
-(* Returns whether the argument is a toplevel expression. *)
-let is_eval = function
-  | { Parsetree.pstr_desc = Parsetree.Pstr_eval _ } -> true
-  | _ -> false
+let rule_path rule =
+  match rule.path_to_rewrite with
+  | Some _ as x -> x
+  | None ->
+    try
+      let env = !Toploop.toplevel_env in
+      let path =
+        match Env.lookup_type rule.type_to_rewrite env with
+        | path, { Types.type_kind     = Types.Type_abstract
+                ; Types.type_private  = Asttypes.Public
+                ; Types.type_manifest = Some ty
+                } -> begin
+            match Ctype.expand_head env ty with
+            | { Types.desc = Types.Tconstr (path, _, _) } -> path
+            | _ -> path
+          end
+        | path, _ -> path
+      in
+      let opt = Some path in
+      rule.path_to_rewrite <- opt;
+      opt
+    with _ ->
+      None
 
 (* Returns whether the given path is persistent. *)
 let rec is_persistent_path = function
@@ -504,38 +517,6 @@ let rec is_persistent_path = function
   | Path.Pdot (p, _, _) -> is_persistent_path p
   | Path.Papply (_, p) -> is_persistent_path p
 
-(* Convert a path to a long identifier. *)
-let rec longident_of_path path =
-  match path with
-    | Path.Pident id ->
-      Longident.Lident (Ident.name id)
-    | Path.Pdot (path, s, _) ->
-      Longident.Ldot (longident_of_path path, s)
-    | Path.Papply (p1, p2) ->
-      Longident.Lapply (longident_of_path p1, longident_of_path p2)
-
-(* Returns the rewrite rule associated to a type, if any. *)
-let rec rule_of_type typ =
-  match typ.Types.desc with
-    | Types.Tlink typ ->
-      rule_of_type typ
-    | Types.Tconstr (path, _, _) -> begin
-      match try Some (Env.find_type path !Toploop.toplevel_env) with Not_found -> None with
-      | Some {
-        Types.type_kind = Types.Type_abstract;
-        Types.type_private = Asttypes.Public;
-        Types.type_manifest = Some typ;
-      } ->
-        rule_of_type typ
-      | _ ->
-        try
-          Some (Hashtbl.find rewrite_rules (longident_of_path path))
-        with Not_found ->
-          None
-    end
-    | _ ->
-      None
-
 (* Check that the given long identifier is present in the environment
    and is persistent. *)
 let is_persistent_in_env longident =
@@ -544,6 +525,30 @@ let is_persistent_in_env longident =
   with Not_found ->
     false
 
+let rule_matches rule path =
+  React.S.value rule.enabled &&
+  (match rule_path rule with
+   | None -> false
+   | Some path' -> Path.same path path') &&
+  List.for_all is_persistent_in_env rule.required_values
+
+(* Returns whether the argument is a toplevel expression. *)
+let is_eval = function
+  | { Parsetree.pstr_desc = Parsetree.Pstr_eval _ } -> true
+  | _ -> false
+
+(* Returns the rewrite rule associated to a type, if any. *)
+let rec rule_of_type typ =
+  match (Ctype.expand_head !Toploop.toplevel_env typ).Types.desc with
+  | Types.Tconstr (path, _, _) -> begin
+      try
+        Some (List.find (fun rule -> rule_matches rule path) rewrite_rules)
+      with _ ->
+        None
+    end
+  | _ ->
+    None
+
 #if OCAML_VERSION < (4, 02, 0)
 let rewrite_str_item pstr_item tstr_item =
   match pstr_item, tstr_item.Typedtree.str_desc with
@@ -552,11 +557,8 @@ let rewrite_str_item pstr_item tstr_item =
        Typedtree.Tstr_eval { Typedtree.exp_type = typ }) -> begin
       match rule_of_type typ with
         | Some rule ->
-          if React.S.value rule.enabled && List.for_all is_persistent_in_env rule.required_values then
-            { Parsetree.pstr_desc = Parsetree.Pstr_eval (rule.rewrite loc e);
-              Parsetree.pstr_loc = loc }
-          else
-            pstr_item
+          { Parsetree.pstr_desc = Parsetree.Pstr_eval (rule.rewrite loc e);
+            Parsetree.pstr_loc = loc }
         | None ->
           pstr_item
     end
@@ -570,11 +572,8 @@ let rewrite_str_item pstr_item tstr_item =
        Typedtree.Tstr_eval ({ Typedtree.exp_type = typ }, _)) -> begin
       match rule_of_type typ with
         | Some rule ->
-          if React.S.value rule.enabled && List.for_all is_persistent_in_env rule.required_values then
-            { Parsetree.pstr_desc = Parsetree.Pstr_eval (rule.rewrite loc e, []);
-              Parsetree.pstr_loc = loc }
-          else
-            pstr_item
+          { Parsetree.pstr_desc = Parsetree.Pstr_eval (rule.rewrite loc e, []);
+            Parsetree.pstr_loc = loc }
         | None ->
           pstr_item
     end