diff --git a/test/lwt/echo_server.ml b/test/lwt/echo_server.ml
index 722bcf69..e58a6a01 100644
--- a/test/lwt/echo_server.ml
+++ b/test/lwt/echo_server.ml
@@ -3,6 +3,7 @@ module M_lwt = Moonpool_lwt
 module Trace = Trace_core
 
 let ( let@ ) = ( @@ )
+let await_lwt = M_lwt.await_lwt
 let spf = Printf.sprintf
 
 let str_of_sockaddr = function
@@ -10,31 +11,34 @@ let str_of_sockaddr = function
   | Unix.ADDR_INET (addr, port) ->
     spf "%s:%d" (Unix.string_of_inet_addr addr) port
 
-let main ~port ~runner () : unit Lwt.t =
+let main ~port ~runner:_ () : unit Lwt.t =
   let@ _sp = Trace.with_span ~__FILE__ ~__LINE__ "main" in
 
   let lwt_fut, _lwt_prom = Lwt.wait () in
 
-  (* TODO: handle exit?? *)
+  (* TODO: handle exit?? ctrl-c? *)
   Printf.printf "listening on port %d\n%!" port;
 
-  let handle_client client_addr ic oc =
+  let handle_client client_addr (ic, oc) : _ Lwt.t =
+    let@ () = M_lwt.spawn_lwt in
     let _sp =
-      Trace.enter_manual_toplevel_span ~__FILE__ ~__LINE__ "handle.client"
+      Trace.enter_manual_span ~parent:None ~__FILE__ ~__LINE__ "handle.client"
         ~data:(fun () -> [ "addr", `String (str_of_sockaddr client_addr) ])
     in
 
+    Printf.printf "got new client\n%!";
+
     let buf = Bytes.create 32 in
     let continue = ref true in
     while !continue do
       Trace.message "read";
-      let n = M_lwt.IO_in.input ic buf 0 (Bytes.length buf) in
+      let n = Lwt_io.read_into ic buf 0 (Bytes.length buf) |> await_lwt in
       if n = 0 then
         continue := false
       else (
         Trace.messagef (fun k -> k "got %dB" n);
-        M_lwt.IO_out.output oc buf 0 n;
-        M_lwt.IO_out.flush oc;
+        Lwt_io.write_from_exactly oc buf 0 n |> await_lwt;
+        Lwt_io.flush oc |> await_lwt;
         Trace.message "write"
       )
     done;
@@ -43,7 +47,9 @@ let main ~port ~runner () : unit Lwt.t =
   in
 
   let addr = Unix.ADDR_INET (Unix.inet_addr_any, port) in
-  let _server = M_lwt.TCP_server.establish ~runner addr handle_client in
+  let _server =
+    Lwt_io.establish_server_with_client_address addr handle_client
+  in
 
   lwt_fut