diff --git a/examples/echo/dune b/examples/echo/dune
index 7fa6bea..99959c7 100644
--- a/examples/echo/dune
+++ b/examples/echo/dune
@@ -1,4 +1,4 @@
 (executable
  (name echo)
- (libraries nanoev nanoev.unix moonpool moonpool.fib trace trace-tef
-   nanoev_tiny_httpd))
+ (libraries nanoev nanoev.unix nanoev-posix moonpool moonpool.fib trace
+   trace-tef nanoev_tiny_httpd))
diff --git a/examples/echo/echo.ml b/examples/echo/echo.ml
index a5543b7..330897f 100644
--- a/examples/echo/echo.ml
+++ b/examples/echo/echo.ml
@@ -86,6 +86,13 @@ let () =
   let port_ = ref 8080 in
   let max_conn = ref 1024 in
   let j = ref 8 in
+  let backend = ref `Posix in
+
+  let set_backend = function
+    | "posix" | "poll" | "default" -> backend := `Posix
+    | "unix" | "select" -> backend := `Unix
+    | s -> failwith @@ Printf.sprintf "unknown backend %S" s
+  in
   Arg.parse
     (Arg.align
        [
@@ -94,15 +101,30 @@ let () =
          "-j", Arg.Set_int j, " number of threads";
          "--debug", Arg.Unit setup_logging, " enable debug";
          "--max-conns", Arg.Set_int max_conn, " maximum concurrent connections";
+         ( "--backend",
+           Arg.Symbol
+             ([ "posix"; "default"; "unix"; "select"; "poll" ], set_backend),
+           " event loop backend" );
        ])
     (fun _ -> raise (Arg.Bad ""))
     "echo [option]*";
 
-  let@ pool = Moonpool.Ws_pool.with_ ~num_threads:!j () in
-  let@ _runner = Moonpool_fib.main in
+  let@ pool =
+   fun yield ->
+    if !j > 1 then
+      let@ pool = Moonpool.Ws_pool.with_ ~num_threads:!j () in
+      let@ _runner = Moonpool_fib.main in
+      yield pool
+    else
+      Moonpool_fib.main yield
+  in
 
-  let ev = Nanoev_unix.create () in
-  Nanoev_picos.setup_bg_thread ev;
+  let ev =
+    match !backend with
+    | `Posix -> Nanoev_posix.create ()
+    | `Unix -> Nanoev_unix.create ()
+  in
+  let@ () = Nanoev_picos.with_setup_bg_thread ev in
 
   let server =
     Nanoev_tiny_httpd.create ~new_thread:(Moonpool.run_async pool) ~port:!port_
@@ -273,8 +295,9 @@ let () =
       let s = to_string_top h in
       Response.make_string ~headers:[ "content-type", "text/html" ] @@ Ok s);
 
-  Printf.printf "listening on http://%s:%d\n%!" (Server.addr server)
-    (Server.port server);
+  Printf.printf
+    "listening on http://%s:%d with %d threads, %d max connections\n%!"
+    (Server.addr server) (Server.port server) !j !max_conn;
   match Server.run server with
   | Ok () -> ()
   | Error e -> raise e
diff --git a/tests/posix/dune b/tests/posix/dune
new file mode 100644
index 0000000..08e8e1a
--- /dev/null
+++ b/tests/posix/dune
@@ -0,0 +1,3 @@
+(tests
+ (names t1)
+ (libraries nanoev nanoev-posix threads))
diff --git a/tests/posix/t1.expected b/tests/posix/t1.expected
new file mode 100644
index 0000000..a36183e
--- /dev/null
+++ b/tests/posix/t1.expected
@@ -0,0 +1,3 @@
+writing
+can read
+done writing
diff --git a/tests/posix/t1.ml b/tests/posix/t1.ml
new file mode 100644
index 0000000..366a5c9
--- /dev/null
+++ b/tests/posix/t1.ml
@@ -0,0 +1,29 @@
+module E = Nanoev_posix
+
+let mkpipe () : Unix.file_descr * Unix.file_descr =
+  let f1, f2 = Unix.pipe () in
+  Unix.set_nonblock f1;
+  Unix.set_nonblock f2;
+  f1, f2
+
+let loop (e : E.t) =
+  while true do
+    E.step e
+  done
+
+let () =
+  let ev = E.create () in
+  ignore (Thread.create loop ev : Thread.t);
+  let rd, wr = mkpipe () in
+  E.on_readable ev rd () () (fun ~closed () () ->
+      if closed then
+        print_endline "closed!"
+      else
+        print_endline "can read");
+  Thread.delay 0.05;
+  print_endline "writing";
+  ignore
+    (Unix.write wr (Bytes.unsafe_of_string "hello") 0 (String.length "hello")
+      : int);
+  Thread.delay 0.1;
+  print_endline "done writing"