diff --git a/cohttp-eio/src/header.ml b/cohttp-eio/src/header.ml
index 86afe3872..25bf9c01a 100644
--- a/cohttp-eio/src/header.ml
+++ b/cohttp-eio/src/header.ml
@@ -21,18 +21,9 @@ type 'a encoder = 'a -> value
 type 'a undecoded = 'a Lazy.t
 type (_, _) eq = Eq : ('a, 'a) eq
 
-module Codec = struct
-  class type t =
-    object
-      method header : 'a. lname -> 'a header
-      method equal : 'a 'b. 'a header -> 'b header -> ('a, 'b) eq option
-      method decoder : 'a. 'a header -> 'a decoder
-      method encoder : 'a. 'a header -> 'a encoder
-      method name : 'a. 'a header -> name
-    end
-
-  let int_decoder v = int_of_string v
-  let int_encoder v = string_of_int v
+class codec =
+  let int_decoder v = int_of_string v in
+  let int_encoder v = string_of_int v in
 
   (* Transfer-Encoding decoder. *)
   let te_decoder v =
@@ -46,7 +37,7 @@ module Codec = struct
            | "deflate" -> `deflate
            | "gzip" -> `gzip
            | v -> failwith @@ "Invalid 'Transfer-Encoding' value " ^ v)
-
+  in
   (* Transfer-Encoding encoder. *)
   let te_encoder v =
     List.map
@@ -57,69 +48,67 @@ module Codec = struct
         | `gzip -> "gzip")
       v
     |> String.concat ", "
-
+  in
   let constructor_name hdr =
     let nm = Obj.Extension_constructor.of_val hdr in
     Obj.Extension_constructor.name nm
+  in
+  object
+    method header : 'a. lname -> 'a header =
+      function
+      | "content-length" -> Obj.magic Content_length
+      | "transfer-encoding" -> Obj.magic Transfer_encoding
+      | h -> Obj.magic (H h)
+
+    method equal : type a b. a header -> b header -> (a, b) eq option =
+      fun a b ->
+        match (a, b) with
+        | Content_length, Content_length -> Some Eq
+        | Transfer_encoding, Transfer_encoding -> Some Eq
+        | H a, H b -> if String.equal a b then Some Eq else None
+        | _ -> None
+
+    method decoder : type a. a header -> a decoder =
+      function
+      | Content_length -> int_decoder
+      | Transfer_encoding -> te_decoder
+      | H _ -> Fun.id
+      | hdr ->
+          let err = "decoder undefined for header " ^ constructor_name hdr in
+          raise @@ Invalid_argument err
+
+    method encoder : type a. a header -> a encoder =
+      function
+      | Content_length -> int_encoder
+      | Transfer_encoding -> te_encoder
+      | H _ -> Fun.id
+      | hdr ->
+          let err = "encoder undefined for header " ^ constructor_name hdr in
+          raise @@ Invalid_argument err
+
+    method name : type a. a header -> name =
+      function
+      | Content_length -> "Content-Length"
+      | Transfer_encoding -> "Transfer-Encoding"
+      | H name -> canonical_name name
+      | hdr ->
+          let err = "name undefined for header " ^ constructor_name hdr in
+          raise @@ Invalid_argument err
+  end
 
-  let v : t =
-    object
-      method header : 'a. lname -> 'a header =
-        function
-        | "content-length" -> Obj.magic Content_length
-        | "transfer-encoding" -> Obj.magic Transfer_encoding
-        | h -> Obj.magic (H h)
-
-      method equal : type a b. a header -> b header -> (a, b) eq option =
-        fun a b ->
-          match (a, b) with
-          | Content_length, Content_length -> Some Eq
-          | Transfer_encoding, Transfer_encoding -> Some Eq
-          | H a, H b -> if String.equal a b then Some Eq else None
-          | _ -> None
-
-      method decoder : type a. a header -> a decoder =
-        function
-        | Content_length -> int_decoder
-        | Transfer_encoding -> te_decoder
-        | H _ -> Fun.id
-        | hdr ->
-            let err = "decoder undefined for header " ^ constructor_name hdr in
-            raise @@ Invalid_argument err
-
-      method encoder : type a. a header -> a encoder =
-        function
-        | Content_length -> int_encoder
-        | Transfer_encoding -> te_encoder
-        | H _ -> Fun.id
-        | hdr ->
-            let err = "encoder undefined for header " ^ constructor_name hdr in
-            raise @@ Invalid_argument err
-
-      method name : type a. a header -> name =
-        function
-        | Content_length -> "Content-Length"
-        | Transfer_encoding -> "Transfer-Encoding"
-        | H name -> canonical_name name
-        | hdr ->
-            let err = "name undefined for header " ^ constructor_name hdr in
-            raise @@ Invalid_argument err
-    end
-end
-
-let name (c : #Codec.t) = c#name
+let name (c : #codec) = c#name
 
 type v = V : 'a header * 'a Lazy.t -> v
 
-class type virtual t =
+class virtual t =
   object
-    inherit Codec.t
+    inherit codec
     method virtual headers : v list Atomic.t
     method virtual to_list : v list
     method virtual modify : (v list -> v list) -> unit
   end
 
-let make_n (c : #Codec.t) values : t =
+let make_n (c : #codec) values : t =
   let headers = Atomic.make values in
   let rec modify f r =
     let v_old = Atomic.get r in
@@ -139,7 +128,7 @@ let make_n (c : #Codec.t) values : t =
 
 let make code = make_n code []
 
-let of_name_values (c : #Codec.t) l =
+let of_name_values (c : #codec) l =
   List.map
     (fun (name, value) ->
       let h = c#header (lname name) in
@@ -164,9 +153,7 @@ let add_name_value (t : t) ~name ~value =
   let v = lazy (t#decoder h value) in
   add_lazy t h v
 
-let encode : type a. #Codec.t -> a header -> a -> string =
- fun codec h v -> codec#encoder h v
-
+let encode : type a. t -> a header -> a -> string = fun t h v -> t#encoder h v
 let decode : type a. a undecoded -> a = Lazy.force
 
 let exists (t : #t) (f : < f : 'a. 'a header -> 'a undecoded -> bool >) =
diff --git a/cohttp-eio/src/header.mli b/cohttp-eio/src/header.mli
index d720c46a2..d1fca515a 100644
--- a/cohttp-eio/src/header.mli
+++ b/cohttp-eio/src/header.mli
@@ -43,9 +43,9 @@ type 'a header = ..
       or found.
 
     Users should extend this type to define custom headers along with a custom
-    {!class:Codec.t} instance.
+    {!class:codec} instance.
 
-    See {!class:Codec.t}. *)
+    See {!class:codec}. *)
 
 type 'a header +=
   | Content_length : int header
@@ -65,15 +65,20 @@ type 'a undecoded
 (** ['a undecoded] represents a lazy value that is as yet undecoded. See
     {!val:decode}. *)
 
-(** [eq] is the OCaml GADT equality. *)
+(** [eq] is OCaml GADT equality. *)
 type (_, _) eq = Eq : ('a, 'a) eq
 
-(** {1 Codec}
+(** {2 codec}
 
-    [Codec] defines encoders, decoders and equality for {!type:header}.
+    [codec] defines encoders, decoders and equality for the following HTTP
+    headers:
+
+    - {!val:Content_Length}
+    - {!val:Transfer_encoding}
+    - {!val:H}
 
     Users looking to combine both custom headers and headers defined in this
-    module should implement {!type:Codec.t} and use {!val:Codec.v}.
+    module are recommended to inherit this class.
 
     {i Example} Here we define two custom headers [Header1] and [Header2] and
     implement codec for it in object [custom_codec].
@@ -83,88 +88,87 @@ type (_, _) eq = Eq : ('a, 'a) eq
         | Header1 : string Header.header
         | Header2 : int Header.header
 
-      let custom_codec : Header.Codec.t =
+      let custom_codec : Header.codec =
         object
-          method header : type a. Header.lname -> a Header.header =
+          inherit Header.codec as super
+
+          method! header : type a. Header.lname -> a Header.header =
             fun nm ->
               match (nm :> string) with
               | "header1" -> Obj.magic Header1
               | "header2" -> Obj.magic Header2
-              | _ -> Header.Codec.v#header nm
+              | _ -> super#header nm
 
-          method equal : type a b.
+          method! equal : type a b.
               a Header.header -> b Header.header -> (a, b) Header.eq option =
             fun a b ->
               match (a, b) with
               | Header1, Header1 -> Some Eq
               | Header2, Header2 -> Some Eq
-              | _ -> Header.Codec.v#equal a b
+              | _ -> super#equal a b
 
-          method decoder : type a. a Header.header -> a Header.decoder =
+          method! decoder : type a. a Header.header -> a Header.decoder =
             function
             | Header1 -> int_of_string
             | Header2 -> float_of_string
-            | hdr -> Header.Codec.v#decoder hdr
+            | hdr -> super#decoder hdr
 
-          method encoder : type a. a Header.header -> a Header.encoder =
+          method! encoder : type a. a Header.header -> a Header.encoder =
             function
             | Header1 -> string_of_int
             | Header2 -> string_of_float
-            | hdr -> Header.Codec.v#encoder hdr
+            | hdr -> super#encoder hdr
 
-          method name : type a. a Header.header -> Header.name =
+          method! name : type a. a Header.header -> Header.name =
             fun hdr ->
               match hdr with
               | Header1 -> Header.canonical_name "header1"
               | Header2 -> Header.canonical_name "header2"
-              | hdr -> Header.Codec.v#name hdr
+              | hdr -> super#name hdr
         end
-    ]} *)
+    ]}
 
-module Codec : sig
-  (** [t] defines the class type that all codecs has to implement. *)
-  class type t =
-    object
-      method header : 'a. lname -> 'a header
-      (** [header lname] converts [lname] to {!type:header}. *)
+    The headers can then used used as such:
 
-      method equal : 'a 'b. 'a header -> 'b header -> ('a, 'b) eq option
-      (** [equal h1 h2] if [Some Eq] if [h1] and [h2] are equal. It is [None]
-          otherwise. *)
-
-      method decoder : 'a. 'a header -> 'a decoder
-      (** [decoder h] is decoder for header [h]. *)
+    {[
+      let h = Header.make custom_codec in
+      Header.add c Header1 1000;
+      Header.add c Header2 100.222
+    ]} *)
+class codec :
+  object
+    method header : 'a. lname -> 'a header
+    (** [header lname] converts [lname] to {!type:header}. *)
 
-      method encoder : 'a. 'a header -> 'a encoder
-      (** [encoder h] is encoder for header [h]. *)
+    method equal : 'a 'b. 'a header -> 'b header -> ('a, 'b) eq option
+    (** [equal h1 h2] if [Some Eq] if [h1] and [h2] are equal. It is [None]
+        otherwise. *)
 
-      method name : 'a. 'a header -> name
-      (** [name h] is the canonical name for header [h]. *)
-    end
+    method decoder : 'a. 'a header -> 'a decoder
+    (** [decoder h] is decoder for header [h]. *)
 
-  val v : t
-  (** [v] defines [codec]s for the following HTTP headers:
+    method encoder : 'a. 'a header -> 'a encoder
+    (** [encoder h] is encoder for header [h]. *)
 
-      - {!val:Content_Length}
-      - {!val:Transfer_encoding}
-      - {!val:H} *)
-end
+    method name : 'a. 'a header -> name
+    (** [name h] is the canonical name for header [h]. *)
+  end
 
-val name : #Codec.t -> 'a header -> name
+val name : #codec -> 'a header -> name
 (** [name codec h] is the canonical name for header [h]. *)
 
 (** {1 Collection of Headers} *)
 
-type t = private < Codec.t ; .. >
+type t = private < codec ; .. >
 (** [t] represents a collection of HTTP headers. {b Note} [t] is concurrency
     safe. *)
 
 (** {2 Create} *)
 
-val make : #Codec.t -> t
+val make : #codec -> t
 (** [make codec] is an empty [t]. *)
 
-val of_name_values : #Codec.t -> (string * string) list -> t
+val of_name_values : #codec -> (string * string) list -> t
 (** [of_name_values codec l] is [t] with header items initialized to [l] such
     that [List.length seq = Header.length t]. *)
 
@@ -192,7 +196,7 @@ val add_name_value : t -> name:lname -> value:value -> unit
 
 (** {2 Encode, Decode} *)
 
-val encode : #Codec.t -> 'a header -> 'a -> value
+val encode : t -> 'a header -> 'a -> value
 (** [encode codec h v] encodes the value of header [h]. The encoder is used as
     defined in [codec]. *)
 
diff --git a/cohttp-eio/tests/header.md b/cohttp-eio/tests/header.md
index 7dee40b74..6219ca53b 100644
--- a/cohttp-eio/tests/header.md
+++ b/cohttp-eio/tests/header.md
@@ -45,39 +45,41 @@ type 'a Cohttp_eio.Header.header +=
     Header1 : int Header.header
   | Header2 : float Header.header
 
-# let custom_codec : Header.Codec.t = object
-  method header : type a. Header.lname -> a Header.header =
+# let custom_codec : Header.codec = 
+  object 
+  inherit Header.codec as super
+  method! header : type a. Header.lname -> a Header.header =
     fun nm ->
     match (nm :> string) with
     | "header1" -> Obj.magic Header1
     | "header2" -> Obj.magic Header2
-    | _ -> Header.Codec.v#header nm
+    | _ -> super#header nm
 
-  method equal: type a b. a Header.header -> b Header.header -> (a, b) Header.eq option =
+  method! equal: type a b. a Header.header -> b Header.header -> (a, b) Header.eq option =
     fun a b ->
       match a, b with
       | Header1, Header1 -> Some Eq
       | Header2, Header2 -> Some Eq
-      | _ -> Header.Codec.v#equal a b
+      | _ -> super#equal a b
 
-  method decoder: type a. a Header.header -> a Header.decoder = function
+  method! decoder: type a. a Header.header -> a Header.decoder = function
     | Header1 -> int_of_string
     | Header2 -> float_of_string
-    | hdr -> Header.Codec.v#decoder hdr
+    | hdr -> super#decoder hdr
 
-  method encoder: type a. a Header.header -> a Header.encoder = function
+  method! encoder: type a. a Header.header -> a Header.encoder = function
     | Header1 -> string_of_int
     | Header2 -> string_of_float
-    | hdr -> Header.Codec.v#encoder hdr
+    | hdr -> super#encoder hdr
 
-  method name: type a. a Header.header -> Header.name =
+  method! name: type a. a Header.header -> Header.name =
     fun hdr -> 
       match hdr with
       | Header1 -> Header.canonical_name "header1"
       | Header2 -> Header.canonical_name "header2"
-      | hdr -> Header.Codec.v#name hdr
+      | hdr -> super#name hdr
   end ;;
-val custom_codec : Header.Codec.t = <obj>
+val custom_codec : Header.codec = <obj>
 
 # let ch = Header.make custom_codec ;;
 val ch : Header.t = <obj>
@@ -123,7 +125,7 @@ val ch : Header.t = <obj>
 `make` 
 
 ```ocaml
-# let t = Header.(make Codec.v) ;;
+# let t = Header.(make (new codec)) ;;
 val t : Header.t = <obj>
 ```