diff --git a/src_plugins/ord/ppx_deriving_ord.cppo.ml b/src_plugins/ord/ppx_deriving_ord.cppo.ml
index c36d57d..0e781d9 100644
--- a/src_plugins/ord/ppx_deriving_ord.cppo.ml
+++ b/src_plugins/ord/ppx_deriving_ord.cppo.ml
@@ -35,10 +35,14 @@ let reduce_compare l =
   | [] -> [%expr 0]
   | x :: xs -> List.fold_left compare_reduce x xs
 
-let wildcard_case int_cases =
+let wildcard_case ?typ int_cases =
   let loc = !Ast_helper.default_loc in
+  let typ = match typ with
+    | Some typ -> typ
+    | None -> [%type: _] (* don't constrain *)
+  in
   Exp.case [%pat? _] [%expr
-    let to_int = [%e Exp.function_ int_cases] in
+    let to_int (x: [%t typ]) = [%e Exp.match_ [%expr x] int_cases] in
     Ppx_deriving_runtime.compare (to_int lhs) (to_int rhs)]
 
 let pattn side typs =
@@ -185,6 +189,24 @@ let sig_of_type ~options ~path type_decl =
 let str_of_type ~options ~path ({ ptype_loc = loc } as type_decl) =
   parse_options options;
   let quoter = Ppx_deriving.create_quoter () in
+  (* Capture type in helper module outside Ppx_deriving_runtime wrapper (added by sanitize).
+     Required for to_int constraint in variant type wildcard_case if the type name
+     conflicts with a Stdlib type from Ppx_deriving_runtime (e.g. bool in test).
+     In that case we must refer to the type being declared, not the one opened by Ppx_deriving_runtime. *)
+  let helper_type =
+    Type.mk ~loc
+      ~params:type_decl.ptype_params
+      ~manifest:(Ppx_deriving.core_type_of_type_decl type_decl)
+      (mkloc "t" loc)
+  in
+  let helper_typ =
+    let name = mkloc (Longident.parse "Ppx_deriving_ord_helper.t") loc in
+    let params = match helper_type.ptype_params with
+      | [] -> []
+      | _ :: _ -> [Typ.any ()] (* match all params with single wildcard *)
+    in
+    Typ.constr name params
+  in
   let comparator =
     match type_decl.ptype_kind, type_decl.ptype_manifest with
     | Ptype_abstract, Some manifest -> expr_of_typ quoter manifest
@@ -208,7 +230,7 @@ let str_of_type ~options ~path ({ ptype_loc = loc } as type_decl) =
           )
       in
       [%expr fun lhs rhs ->
-        [%e Exp.match_ [%expr lhs, rhs] (cases @ [wildcard_case int_cases])]]
+        [%e Exp.match_ [%expr lhs, rhs] (cases @ [wildcard_case ~typ:helper_typ int_cases])]]
     | Ptype_record labels, _ ->
       let exprs =
         labels |> List.map (fun ({ pld_name = { txt = name }; _ } as pld) ->
@@ -235,9 +257,18 @@ let str_of_type ~options ~path ({ ptype_loc = loc } as type_decl) =
       core_type_of_decl ~options ~path type_decl in
   let out_var =
     pvar (Ppx_deriving.mangle_type_decl (`Prefix "compare") type_decl) in
+  let comparator_with_helper =
+    [%expr let module Ppx_deriving_ord_helper =
+           struct
+             [@@@warning "-unused-type-declaration"]
+             [%%i Str.type_ Nonrecursive [helper_type]]
+           end
+           in
+           [%e Ppx_deriving.sanitize ~quoter (eta_expand (polymorphize comparator))]]
+  in
   [Vb.mk ~attrs:[Ppx_deriving.attr_warning [%expr "-39"]]
          (Pat.constraint_ out_var out_type)
-         (Ppx_deriving.sanitize ~quoter (eta_expand (polymorphize comparator)))]
+         comparator_with_helper]
 
 let () =
   Ppx_deriving.(register (create deriver
diff --git a/src_test/eq/test_deriving_eq.cppo.ml b/src_test/eq/test_deriving_eq.cppo.ml
index a2c4674..6a7c0b6 100644
--- a/src_test/eq/test_deriving_eq.cppo.ml
+++ b/src_test/eq/test_deriving_eq.cppo.ml
@@ -131,6 +131,8 @@ and 'a poly_abs_custom = 'a
 module List = struct
   type 'a t = [`Cons of 'a | `Nil]
   [@@deriving eq]
+  type 'a u = Cons of 'a | Nil
+  [@@deriving eq]
 end
 type 'a std_clash = 'a List.t option
 [@@deriving eq]
@@ -148,6 +150,13 @@ let test_result_result ctxt =
   assert_equal ~printer false (eq (Ok "123") (Error 123));
   assert_equal ~printer false (eq (Error 123) (Error 0))
 
+module ResultOverride = struct
+  type t =
+    | Ok
+    | Error
+  [@@deriving eq]
+end
+
 let suite = "Test deriving(eq)" >::: [
     "test_simple"        >:: test_simple;
     "test_array"         >:: test_arr;
diff --git a/src_test/ord/test_deriving_ord.cppo.ml b/src_test/ord/test_deriving_ord.cppo.ml
index fdd4d0d..ab23f9d 100644
--- a/src_test/ord/test_deriving_ord.cppo.ml
+++ b/src_test/ord/test_deriving_ord.cppo.ml
@@ -158,6 +158,8 @@ and 'a poly_abs_custom = 'a
 module List = struct
   type 'a t = [`Cons of 'a | `Nil]
   [@@deriving ord]
+  type 'a u = Cons of 'a | Nil
+  [@@deriving ord]
 end
 type 'a std_clash = 'a List.t option
 [@@deriving ord]
@@ -179,6 +181,13 @@ let test_record_order ctxt =
   assert_equal ~printer (0) (compare_ab { a = 1; b = 2; } { a = 1; b = 2; });
   assert_equal ~printer (1) (compare_ab { a = 2; b = 2; } { a = 1; b = 2; })
 
+module ResultOverride = struct
+  type t =
+    | Ok
+    | Error
+  [@@deriving ord]
+end
+
 let suite = "Test deriving(ord)" >::: [
     "test_simple"        >:: test_simple;
     "test_variant"       >:: test_variant;