diff --git a/src/main.rs b/src/main.rs
index 317bab2..e952c5e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,6 +18,8 @@ use futures::prelude::*;
 use futures::future;
 use tokio_core::reactor::Core;
 use tokio_core::net::UdpSocket;
+use std::cell::RefCell;
+use std::rc::Rc;
 
 const TIMEOUT_SEC: u64 = 10;
 const LOCAL_ADDRESS: &str = "127.0.0.1:3000";
@@ -26,11 +28,11 @@ const SERVER_ADDRESS: &str = "9.9.9.9:53";
 const MIN_DNS_PACKET_LEN: usize = 17;
 const MAX_DNS_QUESTION_LEN: usize = 512;
 const MAX_DNS_RESPONSE_LEN: usize = 4096;
+const MAX_CLIENTS: u32 = 512;
 
 #[derive(Clone, Debug)]
 struct DoH {
     handle: Handle,
-    timers: tokio_timer::Timer,
 }
 
 impl Service for DoH {
@@ -52,9 +54,7 @@ impl Service for DoH {
                             "application/dns-udpwireformat".parse().unwrap(),
                         ))
                 });
-                let timed = self.timers
-                    .timeout(fut.map_err(|_| ()), Duration::from_secs(TIMEOUT_SEC));
-                return Box::new(timed.map_err(|_| hyper::Error::Timeout));
+                return Box::new(fut.map_err(|_| hyper::Error::Incomplete));
             }
             (&Method::Post, _) => {
                 response.set_status(StatusCode::NotFound);
@@ -96,33 +96,40 @@ impl DoH {
 fn main() {
     let mut core = Core::new().unwrap();
     let handle = core.handle();
-
     let addr = LOCAL_ADDRESS.parse().unwrap();
     let handle_inner = handle.clone();
-    let timers = tokio_timer::wheel().build();
-
     let server = Http::new()
         .keep_alive(false)
         .max_buf_size(MAX_DNS_QUESTION_LEN)
         .serve_addr_handle(&addr, &handle, move || {
             Ok(DoH {
                 handle: handle_inner.clone(),
-                timers: timers.clone(),
             })
         })
         .unwrap();
     println!("Listening on http://{}", server.incoming_ref().local_addr());
     let handle_inner = handle.clone();
-    handle.spawn(
-        server
-            .for_each(move |conn| {
-                handle_inner.spawn(
-                    conn.map(|_| ())
-                        .map_err(|err| eprintln!("server error: {:?}", err)),
-                );
-                Ok(())
+    let timers = tokio_timer::wheel().build();
+    let client_count = Rc::new(RefCell::new(0u32));
+    let fut = server.for_each(move |client_fut| {
+        let client_count_inner = client_count.clone();
+        {
+            let count = client_count_inner.borrow_mut();
+            if *count > MAX_CLIENTS {
+                return Ok(());
+            }
+            (*count).saturating_add(1);
+        }
+        let timers_inner = timers.clone();
+        let fut = client_fut
+            .map(move |_| {
+                (*client_count_inner.borrow_mut()).saturating_sub(1);
             })
-            .map_err(|_| ()),
-    );
+            .map_err(|err| eprintln!("server error: {:?}", err));
+        let timed = timers_inner.timeout(fut, Duration::from_secs(TIMEOUT_SEC));
+        handle_inner.spawn(timed);
+        Ok(())
+    });
+    handle.spawn(fut.map_err(|_| ()));
     core.run(futures::future::empty::<(), ()>()).unwrap();
 }