diff --git a/src/ast_builder.mli b/src/ast_builder.mli
index dbf52598..4bbd74d2 100644
--- a/src/ast_builder.mli
+++ b/src/ast_builder.mli
@@ -96,7 +96,8 @@ module type S = sig
 end
 
 (** Build Ast helpers with the location argument factorized. *)
-module Make (_ : Loc) : S
+module Make (Loc : Loc) : S
+[@@ocaml.warning "-67"]
 
 val make : Location.t -> (module S)
 (** Functional version of [Make]. *)
diff --git a/src/driver.mli b/src/driver.mli
index a9944cf8..8d655a22 100644
--- a/src/driver.mli
+++ b/src/driver.mli
@@ -224,6 +224,7 @@ module Create_file_property
     (T : Sexpable.S) : sig
   val set : T.t -> unit
 end
+[@@ocaml.warning "-67"]
 
 val standalone : unit -> unit
 (** Suitable for -pp and also usable as a standalone command line tool.
diff --git a/src/pp_ast.mli b/src/pp_ast.mli
index 1dd4777b..23a67d54 100644
--- a/src/pp_ast.mli
+++ b/src/pp_ast.mli
@@ -83,7 +83,7 @@ end
 module type Configured = S with type 'a printer = 'a configured
 module type Configurable = S with type 'a printer = 'a configurable
 
-module Make (_ : Conf) : Configured
+module Make (Conf : Conf) : Configured [@@ocaml.warning "-67"]
 
 val make : Config.t -> (module Configured)