diff --git a/src/implementation0.ml b/src/implementation0.ml
new file mode 100644
index 0000000..e467adc
--- /dev/null
+++ b/src/implementation0.ml
@@ -0,0 +1,10 @@
+type _ t =
+  | T :
+      { trait : ('t, 'module_type, _) Trait0.t
+      ; impl : 'module_type
+      }
+      -> 't t
+
+let implement (type a i) (trait : (a, i, _) Trait0.t) ~(impl : i) : a t =
+  T { trait; impl }
+;;
diff --git a/src/implementation0.mli b/src/implementation0.mli
new file mode 100644
index 0000000..8f65335
--- /dev/null
+++ b/src/implementation0.mli
@@ -0,0 +1,8 @@
+type _ t = private
+  | T :
+      { trait : ('t, 'module_type, _) Trait0.t
+      ; impl : 'module_type
+      }
+      -> 't t
+
+val implement : ('t, 'module_type, _) Trait0.t -> impl:'module_type -> 't t
diff --git a/src/provider.ml b/src/provider.ml
index 8c24a7d..c0ea41b 100644
--- a/src/provider.ml
+++ b/src/provider.ml
@@ -12,7 +12,7 @@ let raise_s msg sexp = raise (E (Sexp.List [ Atom msg; sexp ]))
 let phys_same t1 t2 = phys_equal (Stdlib.Obj.repr t1) (Stdlib.Obj.repr t2)
 
 module Trait = struct
-  type ('t, 'module_type, 'tag) t = ..
+  type ('t, 'module_type, 'tag) t = ('t, 'module_type, 'tag) Trait0.t = ..
 
   module Info = struct
     type t = Stdlib.Obj.Extension_constructor.t
@@ -50,7 +50,7 @@ module Trait = struct
   module Implementation = struct
     type ('t, 'module_type, 'tag) trait = ('t, 'module_type, 'tag) t
 
-    type _ t =
+    type 'a t = 'a Implementation0.t = private
       | T :
           { trait : ('t, 'module_type, _) trait
           ; impl : 'module_type
@@ -65,9 +65,7 @@ module Trait = struct
     ;;
   end
 
-  let implement (type a i) (trait : (a, i, _) t) ~(impl : i) : a Implementation.t =
-    Implementation.T { trait; impl }
-  ;;
+  let implement = Implementation0.implement
 end
 
 module Interface = struct
diff --git a/src/provider.mli b/src/provider.mli
index ab10ad0..cbae44e 100644
--- a/src/provider.mli
+++ b/src/provider.mli
@@ -29,7 +29,7 @@ module Trait : sig
 
       ['module_type] is expected to be a module type (Eio supports single
       functions but this is discouraged through the use of this library). *)
-  type ('t, 'module_type, 'tag) t = ..
+  type ('t, 'module_type, 'tag) t = ('t, 'module_type, 'tag) Trait0.t = ..
 
   (** {1 Dump & debug} *)
 
@@ -86,7 +86,7 @@ module Trait : sig
 
     type ('t, 'module_type, 'tag) trait := ('t, 'module_type, 'tag) t
 
-    type _ t = private
+    type 'a t = 'a Implementation0.t = private
       | T :
           { trait : ('t, 'module_type, _) trait
           ; impl : 'module_type
diff --git a/src/trait0.ml b/src/trait0.ml
new file mode 100644
index 0000000..e1fb797
--- /dev/null
+++ b/src/trait0.ml
@@ -0,0 +1 @@
+type ('t, 'module_type, 'tag) t = ..
diff --git a/src/trait0.mli b/src/trait0.mli
new file mode 100644
index 0000000..e1fb797
--- /dev/null
+++ b/src/trait0.mli
@@ -0,0 +1 @@
+type ('t, 'module_type, 'tag) t = ..