diff --git a/examples/lwt/lwt_echo_server2.ml b/examples/lwt/lwt_echo_server2.ml
index b27e937..0886a50 100644
--- a/examples/lwt/lwt_echo_server2.ml
+++ b/examples/lwt/lwt_echo_server2.ml
@@ -84,7 +84,7 @@ let connection_handler : Unix.sockaddr -> Lwt_unix.file_descr -> unit Lwt.t =
       in
       (* let (finished, notify) = Lwt.wait () in *)
       let rec on_read _request_data ~off:_ ~len:_ =
-        Body.Writer.flush response_body (fun () ->
+        Body.Writer.flush response_body (fun _ ->
           Body.Reader.schedule_read request_body ~on_eof ~on_read)
       and on_eof () =
         set_interval
@@ -93,13 +93,13 @@ let connection_handler : Unix.sockaddr -> Lwt_unix.file_descr -> unit Lwt.t =
              let _ =
                Body.Writer.write_string response_body "data: some data\n\n"
              in
-             Body.Writer.flush response_body (fun () -> ());
+             Body.Writer.flush response_body ignore;
              true)
           (fun () ->
              let _ =
                Body.Writer.write_string response_body "event: end\ndata: 1\n\n"
              in
-             Body.Writer.flush response_body (fun () ->
+             Body.Writer.flush response_body (fun _ ->
                Body.Writer.close response_body))
       in
       Body.Reader.schedule_read ~on_read ~on_eof request_body;
diff --git a/lib/body.ml b/lib/body.ml
index d786629..9bd6914 100644
--- a/lib/body.ml
+++ b/lib/body.ml
@@ -38,7 +38,6 @@ module Reader = struct
     ; mutable read_scheduled : bool
     ; mutable on_eof : unit -> unit
     ; mutable on_read : Bigstringaf.t -> off:int -> len:int -> unit
-    ; buffered_bytes : int ref
     ; done_reading : int -> unit
     }
 
@@ -51,7 +50,6 @@ module Reader = struct
     ; read_scheduled = false
     ; on_eof = default_on_eof
     ; on_read = default_on_read
-    ; buffered_bytes = ref 0
     ; done_reading
     }
 
@@ -110,12 +108,12 @@ module Writer = struct
 
   type t =
     { faraday : Faraday.t
-    ; buffered_bytes : int ref
+    ; mutable buffered_bytes : int
     ; writer : Serialize.Writer.t
     }
 
   let create buffer ~writer =
-    { faraday = Faraday.of_bigstring buffer; buffered_bytes = ref 0; writer }
+    { faraday = Faraday.of_bigstring buffer; buffered_bytes = 0; writer }
 
   let create_empty ~writer =
     let t = create Bigstringaf.empty ~writer in
@@ -177,17 +175,16 @@ module Writer = struct
       match Faraday.operation faraday with
       | `Yield | `Close -> 0
       | `Writev iovecs ->
-        let buffered = t.buffered_bytes in
-        let iovecs = Httpun_types.IOVec.shiftv iovecs !buffered in
+        let iovecs = Httpun_types.IOVec.shiftv iovecs t.buffered_bytes in
         let lengthv = Httpun_types.IOVec.lengthv iovecs in
         let writev_len = if max_bytes < lengthv then max_bytes else lengthv in
-        buffered := !buffered + writev_len;
+        t.buffered_bytes <- t.buffered_bytes + writev_len;
         let frame_info = Writer.make_frame_info ~max_frame_size stream_id in
         Writer.schedule_iovecs writer frame_info ~len:writev_len iovecs;
         Writer.flush t.writer (function
           | `Closed -> close_and_drain t
           | `Written ->
             Faraday.shift faraday writev_len;
-            buffered := !buffered - writev_len);
+            t.buffered_bytes <- t.buffered_bytes - writev_len);
         writev_len
 end