diff --git a/src/client/mod.rs b/src/client/mod.rs
index 04e9503..13a6966 100644
--- a/src/client/mod.rs
+++ b/src/client/mod.rs
@@ -51,28 +51,28 @@ pub trait Connectable {
 
 impl NewClient {
     pub fn from_socket(left: TcpStream, list: ServerList, handle: Handle)
-            -> Box<Future<Item=Self, Error=()>> {
+            -> impl Future<Item=Self, Error=()> {
         let src_dest = future::result(left.peer_addr())
             .join(future::result(get_original_dest(&left)))
             .map_err(|err| warn!("fail to get original dest: {}", err));
-        Box::new(src_dest.map(move |(src, dest)| {
+        src_dest.map(move |(src, dest)| {
             NewClient {
                 left, src, dest: dest.into(), list, handle,
             }
-        }))
+        })
     }
 }
 
 impl NewClient {
     pub fn retrive_dest(self)
-            -> Box<Future<Item=NewClientWithData, Error=()>> {
+            -> impl Future<Item=NewClientWithData, Error=()> {
         let NewClient { left, src, mut dest, list, handle } = self; 
         let wait = Duration::from_millis(500);
         // try to read TLS ClientHello for
         //   1. --remote-dns: parse host name from SNI
         //   2. --n-parallel: need the whole request to be forwarded
         let read = read_with_timeout(left, vec![0u8; 2048], wait, &handle);
-        let result = read.map(move |(left, mut data, len)| {
+        read.map(move |(left, mut data, len)| {
             let (allow_parallel, pending_data) = if len == 0 {
                 info!("no tls request received before timeout");
                 (false, None)
@@ -101,8 +101,7 @@ impl NewClient {
                 client: NewClient { left, src, dest, list, handle },
                 allow_parallel, pending_data,
             }
-        }).map_err(|err| warn!("fail to read hello from client: {}", err));
-        Box::new(result)
+        }).map_err(|err| warn!("fail to read hello from client: {}", err))
     }
 
     fn connect_server(self, n_parallel: usize, wait_response: bool,
diff --git a/src/main.rs b/src/main.rs
index 1141c43..aedafbb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -82,13 +82,14 @@ fn main() {
     let mut sock_file = None;
     if let Some(http_addr) = args.value_of("web-bind") {
         let monitor = monitor.clone();
-        let serv = if http_addr.starts_with("/") {
+        if http_addr.starts_with("/") {
             let sock = AutoRemoveFile::new(&http_addr);
             let incoming = UnixListener::bind(&sock, &handle)
                 .expect("fail to bind web server")
                 .incoming();
             sock_file = Some(sock);
-            web::run_server(incoming, monitor, &handle)
+            let serv = web::run_server(incoming, monitor, &handle);
+            handle.spawn(serv);
         } else {
             // FIXME: remove duplicate code
             let addr = http_addr.parse()
@@ -96,9 +97,9 @@ fn main() {
             let incoming = TcpListener::bind(&addr, &handle)
                 .expect("fail to bind web server")
                 .incoming();
-            web::run_server(incoming, monitor, &handle)
-        };
-        handle.spawn(serv);
+            let serv = web::run_server(incoming, monitor, &handle);
+            handle.spawn(serv);
+        }
         info!("http run on {}", http_addr);
     }
 
diff --git a/src/monitor/mod.rs b/src/monitor/mod.rs
index 3e657f7..7461ed2 100644
--- a/src/monitor/mod.rs
+++ b/src/monitor/mod.rs
@@ -57,11 +57,11 @@ impl Monitor {
     /// Start monitoring delays.
     /// Returned Future won't return unless error on timer.
     pub fn monitor_delay(&self, probe: u64, handle: &Handle)
-            -> Box<Future<Item=(), Error=()>> {
+            -> impl Future<Item=(), Error=()> {
         let handle = handle.clone();
         let init = test_all(self.clone(), true, &handle);
         let interval = Duration::from_secs(probe);
-        let update = init.and_then(move |monitor| {
+        init.and_then(move |monitor| {
             future::loop_fn((monitor, handle), move |(monitor, handle)| {
                 let wait = Timeout::new(interval, &handle)
                     .expect("error on get timeout from reactor")
@@ -71,17 +71,16 @@ impl Monitor {
                         .map(|monitor| (monitor, handle))
                 }).and_then(|args| Ok(Loop::Continue(args)))
             })
-        }).map_err(|_| ());
-        Box::new(update)
+        }).map_err(|_| ())
     }
 
     /// Start monitoring throughput.
     /// Returned Future won't return unless error on timer.
     pub fn monitor_throughput(&self, handle: &Handle)
-            -> Box<Future<Item=(), Error=()>> {
+            -> impl Future<Item=(), Error=()> {
         let interval = Duration::from_secs(THROUGHPUT_INTERVAL_SECS);
         let handle = handle.clone();
-        let lp = future::loop_fn(self.clone(), move |monitor| {
+        future::loop_fn(self.clone(), move |monitor| {
             for (server, meter) in monitor.meters.borrow_mut().iter_mut() {
                 meter.add_sample(server.traffic());
             }
@@ -89,8 +88,7 @@ impl Monitor {
                 .expect("error on get timeout from reactor")
                 .map_err(|err| panic!("error on timer: {}", err))
                 .map(move |_| Loop::Continue(monitor))
-        });
-        Box::new(lp)
+        })
     }
 
     /// Return average throughputs of all servers in the recent monitor
@@ -115,7 +113,7 @@ fn info_stats(infos: &ServerList) -> String {
 }
 
 fn test_all(monitor: Monitor, init: bool, handle: &Handle)
-        -> Box<Future<Item=Monitor, Error=()>> {
+        -> impl Future<Item=Monitor, Error=()> {
     debug!("testing all servers...");
     let tests: Vec<_> = monitor.servers().into_iter().map(move |server| {
         let test = alive_test(&server, handle).then(move |result| {
@@ -128,15 +126,14 @@ fn test_all(monitor: Monitor, init: bool, handle: &Handle)
         });
         Box::new(test) as Box<Future<Item=(), Error=()>>
     }).collect();
-    let sort = future::join_all(tests).then(move |_| {
+    future::join_all(tests).then(move |_| {
         monitor.resort();
         Ok(monitor)
-    });
-    Box::new(sort)
+    })
 }
 
 fn alive_test(server: &ProxyServer, handle: &Handle)
-        -> Box<Future<Item=Duration, Error=io::Error>> {
+        -> impl Future<Item=Duration, Error=io::Error> {
     let request = [
         0, 17,  // length
         rand::random(), rand::random(),  // transaction ID
@@ -168,10 +165,9 @@ fn alive_test(server: &ProxyServer, handle: &Handle)
         }
     });
     let wait = query.select(timeout).map_err(|(err, _)| err);
-    let delay = wait.and_then(|(result, _)| match result {
+    wait.and_then(|(result, _)| match result {
         Some(stream) => Ok(stream),
         None => Err(io::Error::new(io::ErrorKind::TimedOut, "test timeout")),
-    }).inspect(move |t| debug!("[{}] delay {}ms", tag, t.millis()));
-    Box::new(delay)
+    }).inspect(move |t| debug!("[{}] delay {}ms", tag, t.millis()))
 }
 
diff --git a/src/web/mod.rs b/src/web/mod.rs
index d583c54..4d4d58e 100644
--- a/src/web/mod.rs
+++ b/src/web/mod.rs
@@ -82,12 +82,12 @@ impl Service for StatusPages {
                      .with_header(ContentType::plaintext()),
         };
         debug!("{} {} [{}]", req.method(), req.path(), resp.status());
-        return Box::new(future::ok(resp));
+        Box::new(future::ok(resp))
     }
 }
 
 pub fn run_server<I, S, A>(incoming: I, monitor: Monitor, handle: &Handle)
-        -> Box<Future<Item=(), Error=()>>
+        -> impl Future<Item=(), Error=()>
 where I: Stream<Item=(S, A), Error=io::Error> + 'static,
       S: AsyncRead + AsyncWrite + 'static,
       A: Debug {
@@ -102,13 +102,12 @@ where I: Stream<Item=(S, A), Error=io::Error> + 'static,
     let serve = Http::new()
         .serve_incoming(incoming, new_service);
     let handle = handle.clone();
-    let run = serve.for_each(move |conn| {
+    serve.for_each(move |conn| {
         handle.spawn(
             conn.map(|_| ())
                 .map_err(|err| info!("http: {}", err))
         );
         Ok(())
-    }).map_err(|err| error!("error on http server: {}", err));
-    Box::new(run)
+    }).map_err(|err| error!("error on http server: {}", err))
 }