diff --git a/core/src/connection_reuse.rs b/core/src/connection_reuse.rs
index f2e35842..68287dc0 100644
--- a/core/src/connection_reuse.rs
+++ b/core/src/connection_reuse.rs
@@ -129,7 +129,7 @@ enum PeerState<D, M> where M: StreamMuxer {
     // TODO: stronger Future type
     Pending {
         /// Future that produces the muxer.
-        future: Box<Future<Item = ((D, M), Multiaddr), Error = IoError>>,
+        future: Box<Future<Item = ((D, M), Multiaddr), Error = IoError> + Send>,
         /// All the tasks to notify when `future` resolves.
         notify: FnvHashMap<usize, task::Task>,
     },
@@ -164,15 +164,19 @@ where
 
 impl<T, D, M> Transport for ConnectionReuse<T, D, M>
 where
-    T: Transport + 'static, // TODO: 'static :(
+    T: Transport + Send + 'static, // TODO: 'static :(
+    T::Dial: Send,
+    T::MultiaddrFuture: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
     T: Transport<Output = (D, M)> + Clone + 'static, // TODO: 'static :(
-    M: StreamMuxer + 'static,
-    D: Clone + 'static,
+    M: Send + Sync + StreamMuxer + 'static,
+    D: Send + Clone + 'static,
     T: Clone,
 {
     type Output = (D, ConnectionReuseSubstream<T, D, M>);
     type MultiaddrFuture = future::FutureResult<Multiaddr, IoError>;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
     type ListenerUpgrade = FutureResult<(Self::Output, Self::MultiaddrFuture), IoError>;
     type Dial = ConnectionReuseDial<T, D, M>;
 
@@ -245,10 +249,14 @@ where
 
 impl<T, D, M> MuxedTransport for ConnectionReuse<T, D, M>
 where
-    T: Transport + 'static, // TODO: 'static :(
+    T: Transport + Send + 'static, // TODO: 'static :(
+    T::Dial: Send,
+    T::MultiaddrFuture: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
     T: Transport<Output = (D, M)> + Clone + 'static, // TODO: 'static :(
-    M: StreamMuxer + 'static,
-    D: Clone + 'static,
+    M: Send + Sync + StreamMuxer + 'static,
+    D: Send + Clone + 'static,
     T: Clone,
 {
     type Incoming = ConnectionReuseIncoming<T, D, M>;
@@ -305,10 +313,10 @@ where
 impl<T, D, M> Future for ConnectionReuseDial<T, D, M>
 where 
     T: Transport<Output = (D, M)> + Clone,
-    M: StreamMuxer + 'static,
-    D: Clone + 'static,
-    <T as Transport>::Dial: 'static,
-    <T as Transport>::MultiaddrFuture: 'static,
+    M: Send + StreamMuxer + 'static,
+    D: Send + Clone + 'static,
+    <T as Transport>::Dial: Send + 'static,
+    <T as Transport>::MultiaddrFuture: Send + 'static,
 {
     type Item = ((D, ConnectionReuseSubstream<T, D, M>), FutureResult<Multiaddr, IoError>);
     type Error = IoError;
@@ -471,7 +479,7 @@ where
     /// Identifier for this listener. Used to determine which connections were opened by it.
     listener_id: u64,
     /// Opened connections that need to be upgraded.
-    current_upgrades: FuturesUnordered<Box<Future<Item = (T::Output, Multiaddr), Error = IoError>>>,
+    current_upgrades: FuturesUnordered<Box<Future<Item = (T::Output, Multiaddr), Error = IoError> + Send>>,
 
     /// Shared between the whole connection reuse mechanism.
     shared: Arc<Mutex<Shared<T, D, M>>>,
@@ -484,7 +492,7 @@ where
     M: StreamMuxer,
     D: Clone,
     L: Stream<Item = Lu, Error = IoError>,
-    Lu: Future<Item = (T::Output, Multiaddr), Error = IoError> + 'static,
+    Lu: Future<Item = (T::Output, Multiaddr), Error = IoError> + Send + 'static,
 {
     type Item = FutureResult<((D, ConnectionReuseSubstream<T, D, M>), FutureResult<Multiaddr, IoError>), IoError>;
     type Error = IoError;
diff --git a/core/src/swarm.rs b/core/src/swarm.rs
index 35f58857..f7d95ee5 100644
--- a/core/src/swarm.rs
+++ b/core/src/swarm.rs
@@ -41,7 +41,7 @@ pub fn swarm<T, H, F>(
 ) -> (SwarmController<T, F::Future>, SwarmEvents<T, F::Future, H>)
 where
     T: MuxedTransport + Clone + 'static, // TODO: 'static :-/
-    H: FnMut(T::Output, Box<Future<Item = Multiaddr, Error = IoError>>) -> F,
+    H: FnMut(T::Output, Box<Future<Item = Multiaddr, Error = IoError> + Send>) -> F,
     F: IntoFuture<Item = (), Error = IoError>,
 {
     let shared = Arc::new(Mutex::new(Shared {
@@ -105,6 +105,11 @@ where
 impl<T, F> SwarmController<T, F>
 where
     T: MuxedTransport + Clone + 'static, // TODO: 'static :-/
+    T::Dial: Send,
+    T::MultiaddrFuture: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::Output: Send,
     F: 'static,
 {
     /// Asks the swarm to dial the node with the given multiaddress. The connection is then
@@ -119,6 +124,8 @@ where
         -> Result<impl Future<Item = (), Error = IoError>, Multiaddr>
     where
         Du: Transport + 'static, // TODO: 'static :-/
+        Du::Dial: Send,
+        Du::MultiaddrFuture: Send,
         Du::Output: Into<T::Output>,
     {
         self.dial_then(multiaddr, transport, |v| v)
@@ -132,8 +139,10 @@ where
         -> Result<impl Future<Item = (), Error = IoError>, Multiaddr>
     where
         Du: Transport + 'static, // TODO: 'static :-/
+        Du::Dial: Send,
+        Du::MultiaddrFuture: Send,
         Du::Output: Into<T::Output>,
-        TThen: FnOnce(Result<(), IoError>) -> Result<(), IoError> + 'static,
+        TThen: FnOnce(Result<(), IoError>) -> Result<(), IoError> + Send + 'static,
     {
         trace!("Swarm dialing {}", multiaddr);
 
@@ -148,12 +157,12 @@ where
                 let mut then = Box::new(move |val: Result<(), IoError>| {
                     let then = then.take().expect("The Boxed FnMut should only be called once");
                     then(val);
-                }) as Box<FnMut(_)>;
+                }) as Box<FnMut(_) + Send>;
 
                 let dial = dial.then(|result| {
                     match result {
                         Ok((output, client_addr)) => {
-                            let client_addr = Box::new(client_addr) as Box<Future<Item = _, Error = _>>;
+                            let client_addr = Box::new(client_addr) as Box<Future<Item = _, Error = _> + Send>;
                             Ok((output.into(), then, client_addr))
                         }
                         Err(err) => {
@@ -206,12 +215,12 @@ where
                 let listener = Box::new(
                     listener.map(|f| {
                         let f = f.map(|(out, maf)| {
-                            (out, Box::new(maf) as Box<Future<Item = Multiaddr, Error = IoError>>)
+                            (out, Box::new(maf) as Box<Future<Item = Multiaddr, Error = IoError> + Send>)
                         });
 
-                        Box::new(f) as Box<Future<Item = _, Error = _>>
+                        Box::new(f) as Box<Future<Item = _, Error = _> + Send>
                     }),
-                ) as Box<Stream<Item = _, Error = _>>;
+                ) as Box<Stream<Item = _, Error = _> + Send>;
                 shared.listeners.push((new_addr.clone(), listener.into_future()));
                 if let Some(task) = shared.task_to_notify.take() {
                     task.notify();
@@ -242,7 +251,9 @@ where
 impl<T, H, If, F> Stream for SwarmEvents<T, F, H>
 where
     T: MuxedTransport + Clone + 'static, // TODO: 'static :-/,
-    H: FnMut(T::Output, Box<Future<Item = Multiaddr, Error = IoError>>) -> If,
+    T::MultiaddrFuture: Send,
+    T::IncomingUpgrade: Send,
+    H: FnMut(T::Output, Box<Future<Item = Multiaddr, Error = IoError> + Send>) -> If,
     If: IntoFuture<Future = F, Item = (), Error = IoError>,
     F: Future<Item = (), Error = IoError> + 'static,        // TODO: 'static :-/
 {
@@ -259,7 +270,7 @@ where
                     debug!("Swarm received new multiplexed incoming connection");
                     shared.next_incoming = self.transport.clone().next_incoming();
                     let connec = connec.map(|(out, maf)| {
-                        (out, Box::new(maf) as Box<Future<Item = Multiaddr, Error = IoError>>)
+                        (out, Box::new(maf) as Box<Future<Item = Multiaddr, Error = IoError> + Send>)
                     });
                     shared.listeners_upgrade.push(Box::new(connec) as Box<_>);
                 }
@@ -393,21 +404,21 @@ struct Shared<T, F> where T: MuxedTransport + 'static {
         StreamFuture<
             Box<
                 Stream<
-                    Item = Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>,
+                    Item = Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError> + Send>), Error = IoError> + Send>,
                     Error = IoError,
-                >,
+                > + Send,
             >,
         >,
     )>,
 
     /// Futures that upgrade an incoming listening connection to a full connection.
     listeners_upgrade:
-        Vec<Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>>,
+        Vec<Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError> + Send>), Error = IoError> + Send>>,
 
     /// Futures that dial a remote address.
     ///
     /// Contains the address we dial, so that we can cancel it if necessary.
-    dialers: Vec<(Multiaddr, Box<Future<Item = (T::Output, Box<FnMut(Result<(), IoError>)>, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>)>,
+    dialers: Vec<(Multiaddr, Box<Future<Item = (T::Output, Box<FnMut(Result<(), IoError>) + Send>, Box<Future<Item = Multiaddr, Error = IoError> + Send>), Error = IoError> + Send>)>,
 
     /// List of futures produced by the swarm closure. Must be processed to the end.
     to_process: Vec<F>,
diff --git a/core/src/transport/and_then.rs b/core/src/transport/and_then.rs
index 94b341bf..dcfb6664 100644
--- a/core/src/transport/and_then.rs
+++ b/core/src/transport/and_then.rs
@@ -40,15 +40,18 @@ pub struct AndThen<T, C> {
 impl<T, C, F, O, Maf> Transport for AndThen<T, C>
 where
     T: Transport + 'static,
-    C: FnOnce(T::Output, Endpoint, T::MultiaddrFuture) -> F + Clone + 'static,
-    F: Future<Item = (O, Maf), Error = IoError> + 'static,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    C: FnOnce(T::Output, Endpoint, T::MultiaddrFuture) -> F + Clone + Send + 'static,
+    F: Future<Item = (O, Maf), Error = IoError> + Send + 'static,
     Maf: Future<Item = Multiaddr, Error = IoError> + 'static,
 {
     type Output = O;
     type MultiaddrFuture = Maf;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError>>;
-    type Dial = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError>>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
+    type ListenerUpgrade = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError> + Send>;
+    type Dial = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
@@ -116,12 +119,17 @@ where
 impl<T, C, F, O, Maf> MuxedTransport for AndThen<T, C>
 where
     T: MuxedTransport + 'static,
-    C: FnOnce(T::Output, Endpoint, T::MultiaddrFuture) -> F + Clone + 'static,
-    F: Future<Item = (O, Maf), Error = IoError> + 'static,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::Incoming: Send,
+    T::IncomingUpgrade: Send,
+    C: FnOnce(T::Output, Endpoint, T::MultiaddrFuture) -> F + Clone + Send + 'static,
+    F: Future<Item = (O, Maf), Error = IoError> + Send + 'static,
     Maf: Future<Item = Multiaddr, Error = IoError> + 'static,
 {
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError>>;
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError> + Send>;
+    type IncomingUpgrade = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn next_incoming(self) -> Self::Incoming {
@@ -134,7 +142,7 @@ where
                 upgrade(connection, Endpoint::Listener, client_addr)
             });
 
-            Box::new(future) as Box<Future<Item = _, Error = _>>
+            Box::new(future) as Box<Future<Item = _, Error = _> + Send>
         });
 
         Box::new(future) as Box<_>
diff --git a/core/src/transport/choice.rs b/core/src/transport/choice.rs
index e977bd8f..78288cf9 100644
--- a/core/src/transport/choice.rs
+++ b/core/src/transport/choice.rs
@@ -85,26 +85,26 @@ impl<A, B> MuxedTransport for OrTransport<A, B>
 where
     A: MuxedTransport,
     B: MuxedTransport,
-    A::Incoming: 'static,        // TODO: meh :-/
-    B::Incoming: 'static,        // TODO: meh :-/
-    A::IncomingUpgrade: 'static, // TODO: meh :-/
-    B::IncomingUpgrade: 'static, // TODO: meh :-/
+    A::Incoming: Send + 'static,        // TODO: meh :-/
+    B::Incoming: Send + 'static,        // TODO: meh :-/
+    A::IncomingUpgrade: Send + 'static, // TODO: meh :-/
+    B::IncomingUpgrade: Send + 'static, // TODO: meh :-/
     A::Output: 'static,          // TODO: meh :-/
     B::Output: 'static,          // TODO: meh :-/
 {
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError> + Send>;
     type IncomingUpgrade =
-        Box<Future<Item = (EitherOutput<A::Output, B::Output>, Self::MultiaddrFuture), Error = IoError>>;
+        Box<Future<Item = (EitherOutput<A::Output, B::Output>, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn next_incoming(self) -> Self::Incoming {
         let first = self.0.next_incoming().map(|out| {
             let fut = out.map(move |(v, addr)| (EitherOutput::First(v), future::Either::A(addr)));
-            Box::new(fut) as Box<Future<Item = _, Error = _>>
+            Box::new(fut) as Box<Future<Item = _, Error = _> + Send>
         });
         let second = self.1.next_incoming().map(|out| {
             let fut = out.map(move |(v, addr)| (EitherOutput::Second(v), future::Either::B(addr)));
-            Box::new(fut) as Box<Future<Item = _, Error = _>>
+            Box::new(fut) as Box<Future<Item = _, Error = _> + Send>
         });
         let future = first.select(second).map(|(i, _)| i).map_err(|(e, _)| e);
         Box::new(future) as Box<_>
diff --git a/core/src/transport/map.rs b/core/src/transport/map.rs
index 77bf43c3..d4e09068 100644
--- a/core/src/transport/map.rs
+++ b/core/src/transport/map.rs
@@ -42,13 +42,16 @@ impl<T, F> Map<T, F> {
 impl<T, F, D> Transport for Map<T, F>
 where
     T: Transport + 'static,                  // TODO: 'static :-/
-    F: FnOnce(T::Output, Endpoint) -> D + Clone + 'static, // TODO: 'static :-/
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    F: FnOnce(T::Output, Endpoint) -> D + Clone + Send + 'static, // TODO: 'static :-/
 {
     type Output = D;
     type MultiaddrFuture = T::MultiaddrFuture;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
+    type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
         let map = self.map;
@@ -91,10 +94,15 @@ where
 impl<T, F, D> MuxedTransport for Map<T, F>
 where
     T: MuxedTransport + 'static,             // TODO: 'static :-/
-    F: FnOnce(T::Output, Endpoint) -> D + Clone + 'static, // TODO: 'static :-/
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::Incoming: Send,
+    T::IncomingUpgrade: Send,
+    F: FnOnce(T::Output, Endpoint) -> D + Clone + Send + 'static, // TODO: 'static :-/
 {
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError> + Send>;
+    type IncomingUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn next_incoming(self) -> Self::Incoming {
         let map = self.map;
diff --git a/core/src/transport/map_err_dial.rs b/core/src/transport/map_err_dial.rs
index c90f7349..f99ff8e9 100644
--- a/core/src/transport/map_err_dial.rs
+++ b/core/src/transport/map_err_dial.rs
@@ -41,13 +41,14 @@ impl<T, F> MapErrDial<T, F> {
 impl<T, F> Transport for MapErrDial<T, F>
 where
     T: Transport + 'static,                          // TODO: 'static :-/
-    F: FnOnce(IoError, Multiaddr) -> IoError + Clone + 'static, // TODO: 'static :-/
+    T::Dial: Send,
+    F: FnOnce(IoError, Multiaddr) -> IoError + Clone + Send + 'static, // TODO: 'static :-/
 {
     type Output = T::Output;
     type MultiaddrFuture = T::MultiaddrFuture;
     type Listener = T::Listener;
     type ListenerUpgrade = T::ListenerUpgrade;
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
         match self.transport.listen_on(addr) {
@@ -77,7 +78,8 @@ where
 impl<T, F> MuxedTransport for MapErrDial<T, F>
 where
     T: MuxedTransport + 'static,                     // TODO: 'static :-/
-    F: FnOnce(IoError, Multiaddr) -> IoError + Clone + 'static, // TODO: 'static :-/
+    T::Dial: Send,
+    F: FnOnce(IoError, Multiaddr) -> IoError + Clone + Send + 'static, // TODO: 'static :-/
 {
     type Incoming = T::Incoming;
     type IncomingUpgrade = T::IncomingUpgrade;
diff --git a/core/src/transport/memory.rs b/core/src/transport/memory.rs
index ffbb2069..2b152dba 100644
--- a/core/src/transport/memory.rs
+++ b/core/src/transport/memory.rs
@@ -50,12 +50,12 @@ impl<T> Clone for Dialer<T> {
     }
 }
 
-impl<T: IntoBuf + 'static> Transport for Dialer<T> {
+impl<T: IntoBuf + Send + 'static> Transport for Dialer<T> {
     type Output = Channel<T>;
-    type Listener = Box<Stream<Item=Self::ListenerUpgrade, Error=io::Error>>;
+    type Listener = Box<Stream<Item=Self::ListenerUpgrade, Error=io::Error> + Send>;
     type ListenerUpgrade = FutureResult<(Self::Output, Self::MultiaddrFuture), io::Error>;
     type MultiaddrFuture = FutureResult<Multiaddr, io::Error>;
-    type Dial = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error>>;
+    type Dial = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error> + Send>;
 
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
         Err((self, addr))
@@ -93,12 +93,12 @@ impl<T> Clone for Listener<T> {
     }
 }
 
-impl<T: IntoBuf + 'static> Transport for Listener<T> {
+impl<T: IntoBuf + Send + 'static> Transport for Listener<T> {
     type Output = Channel<T>;
-    type Listener = Box<Stream<Item=Self::ListenerUpgrade, Error=io::Error>>;
+    type Listener = Box<Stream<Item=Self::ListenerUpgrade, Error=io::Error> + Send>;
     type ListenerUpgrade = FutureResult<(Self::Output, Self::MultiaddrFuture), io::Error>;
     type MultiaddrFuture = FutureResult<Multiaddr, io::Error>;
-    type Dial = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error>>;
+    type Dial = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error> + Send>;
 
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
         if !is_memory_addr(&addr) {
@@ -200,12 +200,12 @@ mod tests {
         #[derive(Clone)]
         struct Echo(mpsc::UnboundedSender<()>);
 
-        impl<Maf: 'static> ConnectionUpgrade<memory::Channel<Bytes>, Maf> for Echo {
+        impl<Maf: Send + 'static> ConnectionUpgrade<memory::Channel<Bytes>, Maf> for Echo {
             type NamesIter = iter::Once<(Bytes, ())>;
             type UpgradeIdentifier = ();
             type Output = ();
             type MultiaddrFuture = Maf;
-            type Future = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error>>;
+            type Future = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error> + Send>;
 
             fn protocol_names(&self) -> Self::NamesIter {
                 iter::once(("/echo/1.0.0".into(), ()))
diff --git a/core/src/transport/upgrade.rs b/core/src/transport/upgrade.rs
index f1a4fd17..8d9fc621 100644
--- a/core/src/transport/upgrade.rs
+++ b/core/src/transport/upgrade.rs
@@ -47,8 +47,15 @@ impl<T, C> UpgradedNode<T, C> {
 impl<'a, T, C> UpgradedNode<T, C>
 where
     T: Transport + 'a,
-    T::Output: AsyncRead + AsyncWrite,
-    C: ConnectionUpgrade<T::Output, T::MultiaddrFuture> + 'a,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: Send + AsyncRead + AsyncWrite,
+    C: ConnectionUpgrade<T::Output, T::MultiaddrFuture> + Send + 'a,
+    C::NamesIter: Send,
+    C::Future: Send,
+    C::UpgradeIdentifier: Send,
 {
     /// Returns a reference to the inner `Transport`.
     #[inline]
@@ -65,7 +72,7 @@ where
     pub fn dial(
         self,
         addr: Multiaddr,
-    ) -> Result<Box<Future<Item = (C::Output, C::MultiaddrFuture), Error = IoError> + 'a>, (Self, Multiaddr)>
+    ) -> Result<Box<Future<Item = (C::Output, C::MultiaddrFuture), Error = IoError> + Send + 'a>, (Self, Multiaddr)>
     where
         C::NamesIter: Clone, // TODO: not elegant
     {
@@ -101,13 +108,15 @@ where
         self,
     ) -> Box<
         Future<
-                Item = Box<Future<Item = (C::Output, C::MultiaddrFuture), Error = IoError> + 'a>,
+                Item = Box<Future<Item = (C::Output, C::MultiaddrFuture), Error = IoError> + Send + 'a>,
                 Error = IoError,
             >
-            + 'a,
+            + Send + 'a,
     >
     where
         T: MuxedTransport,
+        T::Incoming: Send,
+        T::IncomingUpgrade: Send,
         C::NamesIter: Clone, // TODO: not elegant
         C: Clone,
     {
@@ -119,7 +128,7 @@ where
                 apply(connection, upgrade, Endpoint::Listener, client_addr)
             });
 
-            Box::new(future) as Box<Future<Item = _, Error = _>>
+            Box::new(future) as Box<Future<Item = _, Error = _> + Send>
         });
 
         Box::new(future) as Box<_>
@@ -138,9 +147,10 @@ where
         (
             Box<
                 Stream<
-                        Item = Box<Future<Item = (C::Output, C::MultiaddrFuture), Error = IoError> + 'a>,
+                        Item = Box<Future<Item = (C::Output, C::MultiaddrFuture), Error = IoError> + Send + 'a>,
                         Error = IoError,
                     >
+                    + Send
                     + 'a,
             >,
             Multiaddr,
@@ -187,17 +197,22 @@ where
 impl<T, C> Transport for UpgradedNode<T, C>
 where
     T: Transport + 'static,
-    T::Output: AsyncRead + AsyncWrite,
-    C: ConnectionUpgrade<T::Output, T::MultiaddrFuture> + 'static,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: Send + AsyncRead + AsyncWrite,
+    C: ConnectionUpgrade<T::Output, T::MultiaddrFuture> + Clone + Send + 'static,
     C::MultiaddrFuture: Future<Item = Multiaddr, Error = IoError>,
-    C::NamesIter: Clone, // TODO: not elegant
-    C: Clone,
+    C::NamesIter: Clone + Send,
+    C::Future: Send,
+    C::UpgradeIdentifier: Send,
 {
     type Output = C::Output;
     type MultiaddrFuture = C::MultiaddrFuture;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (C::Output, Self::MultiaddrFuture), Error = IoError>>;
-    type Dial = Box<Future<Item = (C::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
+    type ListenerUpgrade = Box<Future<Item = (C::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
+    type Dial = Box<Future<Item = (C::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
@@ -218,14 +233,21 @@ where
 impl<T, C> MuxedTransport for UpgradedNode<T, C>
 where
     T: MuxedTransport + 'static,
-    T::Output: AsyncRead + AsyncWrite,
-    C: ConnectionUpgrade<T::Output, T::MultiaddrFuture> + 'static,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: Send + AsyncRead + AsyncWrite,
+    T::Incoming: Send,
+    T::IncomingUpgrade: Send,
+    C: ConnectionUpgrade<T::Output, T::MultiaddrFuture> + Clone + Send + 'static,
     C::MultiaddrFuture: Future<Item = Multiaddr, Error = IoError>,
-    C::NamesIter: Clone, // TODO: not elegant
-    C: Clone,
+    C::NamesIter: Clone + Send,
+    C::Future: Send,
+    C::UpgradeIdentifier: Send,
 {
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade = Box<Future<Item = (C::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError> + Send>;
+    type IncomingUpgrade = Box<Future<Item = (C::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn next_incoming(self) -> Self::Incoming {
diff --git a/core/src/unique.rs b/core/src/unique.rs
index 084596f0..0e621587 100644
--- a/core/src/unique.rs
+++ b/core/src/unique.rs
@@ -101,10 +101,17 @@ impl<T> UniqueConnec<T> {
     #[inline]
     pub fn dial<S, F, Du>(&self, swarm: &SwarmController<S, F>, multiaddr: &Multiaddr,
                           transport: Du) -> UniqueConnecFuture<T>
-        where T: Clone + 'static,       // TODO: 'static :-/
+        where T: Clone + Send + 'static,       // TODO: 'static :-/
               Du: Transport + 'static, // TODO: 'static :-/
               Du::Output: Into<S::Output>,
+              Du::Dial: Send,
+              Du::MultiaddrFuture: Send,
               S: Clone + MuxedTransport,
+              S::Dial: Send,
+              S::Listener: Send,
+              S::ListenerUpgrade: Send,
+              S::Output: Send,
+              S::MultiaddrFuture: Send,
               F: 'static,
     {
         self.dial_inner(swarm, multiaddr, transport, true)
@@ -115,10 +122,17 @@ impl<T> UniqueConnec<T> {
     #[inline]
     pub fn dial_if_empty<S, F, Du>(&self, swarm: &SwarmController<S, F>, multiaddr: &Multiaddr,
                                    transport: Du) -> UniqueConnecFuture<T>
-        where T: Clone + 'static,       // TODO: 'static :-/
+        where T: Clone + Send + 'static,       // TODO: 'static :-/
               Du: Transport + 'static, // TODO: 'static :-/
               Du::Output: Into<S::Output>,
+              Du::Dial: Send,
+              Du::MultiaddrFuture: Send,
               S: Clone + MuxedTransport,
+              S::Dial: Send,
+              S::Listener: Send,
+              S::ListenerUpgrade: Send,
+              S::Output: Send,
+              S::MultiaddrFuture: Send,
               F: 'static,
     {
         self.dial_inner(swarm, multiaddr, transport, false)
@@ -127,10 +141,17 @@ impl<T> UniqueConnec<T> {
     /// Inner implementation of `dial_*`.
     fn dial_inner<S, F, Du>(&self, swarm: &SwarmController<S, F>, multiaddr: &Multiaddr,
                             transport: Du, dial_if_err: bool) -> UniqueConnecFuture<T>
-        where T: Clone + 'static,       // TODO: 'static :-/
+        where T: Clone + Send + 'static,       // TODO: 'static :-/
               Du: Transport + 'static, // TODO: 'static :-/
               Du::Output: Into<S::Output>,
+              Du::Dial: Send,
+              Du::MultiaddrFuture: Send,
               S: Clone + MuxedTransport,
+              S::Dial: Send,
+              S::Listener: Send,
+              S::ListenerUpgrade: Send,
+              S::Output: Send,
+              S::MultiaddrFuture: Send,
               F: 'static,
     {
         let mut inner = self.inner.lock();
diff --git a/core/src/upgrade/loop_upg.rs b/core/src/upgrade/loop_upg.rs
index f3e67c5d..faf761c0 100644
--- a/core/src/upgrade/loop_upg.rs
+++ b/core/src/upgrade/loop_upg.rs
@@ -64,18 +64,21 @@ pub struct LoopUpg<Inner> {
 impl<State, Socket, Inner, Out, AddrFut> ConnectionUpgrade<(State, Socket), AddrFut>
     for LoopUpg<Inner>
 where
-    State: 'static,
-    Socket: AsyncRead + AsyncWrite + 'static,
+    State: Send + 'static,
+    Socket: AsyncRead + AsyncWrite + Send + 'static,
     Inner: ConnectionUpgrade<
             (State, Socket),
             AddrFut,
             Output = Loop<State, Socket, Out>,
             MultiaddrFuture = AddrFut,
         > + Clone
+        + Send
         + 'static,
-    Inner::NamesIter: Clone + 'static,
-    AddrFut: 'static,
-    Out: 'static,
+    Inner::NamesIter: Clone + Send + 'static,
+    Inner::UpgradeIdentifier: Send,
+    Inner::Future: Send,
+    AddrFut: Send + 'static,
+    Out: Send + 'static,
 {
     type NamesIter = Inner::NamesIter;
     type UpgradeIdentifier = Inner::UpgradeIdentifier;
@@ -86,7 +89,7 @@ where
 
     type Output = Out;
     type MultiaddrFuture = AddrFut;
-    type Future = Box<Future<Item = (Out, Self::MultiaddrFuture), Error = IoError>>;
+    type Future = Box<Future<Item = (Out, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn upgrade(
         self,
diff --git a/core/src/upgrade/map.rs b/core/src/upgrade/map.rs
index 98eb4e3f..92f365ec 100644
--- a/core/src/upgrade/map.rs
+++ b/core/src/upgrade/map.rs
@@ -39,9 +39,9 @@ pub struct Map<U, F> {
 impl<C, U, F, O, Maf> ConnectionUpgrade<C, Maf> for Map<U, F>
 where
     U: ConnectionUpgrade<C, Maf>,
-    U::Future: 'static,     // TODO: 'static :(
+    U::Future: Send + 'static,     // TODO: 'static :(
     C: AsyncRead + AsyncWrite,
-    F: FnOnce(U::Output) -> O + 'static,     // TODO: 'static :(
+    F: FnOnce(U::Output) -> O + Send + 'static,     // TODO: 'static :(
 {
     type NamesIter = U::NamesIter;
     type UpgradeIdentifier = U::UpgradeIdentifier;
@@ -52,7 +52,7 @@ where
 
     type Output = O;
     type MultiaddrFuture = U::MultiaddrFuture;
-    type Future = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError>>;
+    type Future = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn upgrade(
         self,
diff --git a/core/src/upgrade/map_addr.rs b/core/src/upgrade/map_addr.rs
index 9a60fb02..4b6de993 100644
--- a/core/src/upgrade/map_addr.rs
+++ b/core/src/upgrade/map_addr.rs
@@ -42,11 +42,11 @@ pub struct MapAddr<U, F> {
 impl<C, U, F, O, Maf> ConnectionUpgrade<C, Maf> for MapAddr<U, F>
 where
     U: ConnectionUpgrade<C, Maf>,
-    U::Future: 'static,     // TODO: 'static :(
-    U::MultiaddrFuture: Future<Item = Multiaddr, Error = IoError> + 'static,    // TODO: 'static :(
-    U::Output: 'static,     // TODO: 'static :(
+    U::Future: Send + 'static,     // TODO: 'static :(
+    U::MultiaddrFuture: Future<Item = Multiaddr, Error = IoError> + Send + 'static,    // TODO: 'static :(
+    U::Output: Send + 'static,     // TODO: 'static :(
     C: AsyncRead + AsyncWrite,
-    F: FnOnce(U::Output, &Multiaddr) -> O + 'static,     // TODO: 'static :(
+    F: FnOnce(U::Output, &Multiaddr) -> O + Send + 'static,     // TODO: 'static :(
 {
     type NamesIter = U::NamesIter;
     type UpgradeIdentifier = U::UpgradeIdentifier;
@@ -57,7 +57,7 @@ where
 
     type Output = O;
     type MultiaddrFuture = future::FutureResult<Multiaddr, IoError>;
-    type Future = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError>>;
+    type Future = Box<Future<Item = (O, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn upgrade(
         self,
diff --git a/misc/multistream-select/Cargo.toml b/misc/multistream-select/Cargo.toml
index 3a9c3fc3..fcdcb6d0 100644
--- a/misc/multistream-select/Cargo.toml
+++ b/misc/multistream-select/Cargo.toml
@@ -10,7 +10,7 @@ futures = { version = "0.1" }
 log = "0.4"
 smallvec = "0.5"
 tokio-io = "0.1"
-unsigned-varint = { version = "0.2", features = ["codec"] }
+unsigned-varint = { version = "0.2.1", features = ["codec"] }
 
 [dev-dependencies]
 tokio-current-thread = "0.1"
diff --git a/muxers/mplex/Cargo.toml b/muxers/mplex/Cargo.toml
index 4692f251..0f2fbf82 100644
--- a/muxers/mplex/Cargo.toml
+++ b/muxers/mplex/Cargo.toml
@@ -13,7 +13,7 @@ log = "0.4"
 parking_lot = "0.6"
 tokio-codec = "0.1"
 tokio-io = "0.1"
-unsigned-varint = { version = "0.2", features = ["codec"] }
+unsigned-varint = { version = "0.2.1", features = ["codec"] }
 
 [dev-dependencies]
 libp2p-tcp-transport = { path = "../../transports/tcp" }
diff --git a/protocols/floodsub/Cargo.toml b/protocols/floodsub/Cargo.toml
index e543b52a..6c696e8a 100644
--- a/protocols/floodsub/Cargo.toml
+++ b/protocols/floodsub/Cargo.toml
@@ -18,4 +18,4 @@ protobuf = "2.0.2"
 smallvec = "0.6.0"
 tokio-codec = "0.1"
 tokio-io = "0.1"
-unsigned-varint = { version = "0.2", features = ["codec"] }
+unsigned-varint = { version = "0.2.1", features = ["codec"] }
diff --git a/protocols/floodsub/src/lib.rs b/protocols/floodsub/src/lib.rs
index f90fb127..f2b74c4b 100644
--- a/protocols/floodsub/src/lib.rs
+++ b/protocols/floodsub/src/lib.rs
@@ -91,8 +91,8 @@ impl FloodSubUpgrade {
 
 impl<C, Maf> ConnectionUpgrade<C, Maf> for FloodSubUpgrade
 where
-    C: AsyncRead + AsyncWrite + 'static,
-    Maf: Future<Item = Multiaddr, Error = IoError> + 'static,
+    C: AsyncRead + AsyncWrite + Send + 'static,
+    Maf: Future<Item = Multiaddr, Error = IoError> + Send + 'static,
 {
     type NamesIter = iter::Once<(Bytes, Self::UpgradeIdentifier)>;
     type UpgradeIdentifier = ();
@@ -104,7 +104,7 @@ where
 
     type Output = FloodSubFuture;
     type MultiaddrFuture = future::FutureResult<Multiaddr, IoError>;
-    type Future = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Future = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn upgrade(
@@ -208,7 +208,7 @@ where
                                     // TODO: what if multiple connections?
                                     inner.remote_connections.write().remove(&remote_addr);
                                     let future = future::ok(future::Loop::Break(()));
-                                    Box::new(future) as Box<Future<Item = _, Error = _>>
+                                    Box::new(future) as Box<Future<Item = _, Error = _> + Send>
                                 }
                             }
                         })
@@ -521,7 +521,7 @@ pub struct Message {
 /// Implementation of `Future` that must be driven to completion in order for floodsub to work.
 #[must_use = "futures do nothing unless polled"]
 pub struct FloodSubFuture {
-    inner: Box<Future<Item = (), Error = IoError>>,
+    inner: Box<Future<Item = (), Error = IoError> + Send>,
 }
 
 impl Future for FloodSubFuture {
diff --git a/protocols/identify/Cargo.toml b/protocols/identify/Cargo.toml
index 1df3e221..365bf099 100644
--- a/protocols/identify/Cargo.toml
+++ b/protocols/identify/Cargo.toml
@@ -16,7 +16,7 @@ parking_lot = "0.6"
 protobuf = "2.0.2"
 tokio-codec = "0.1"
 tokio-io = "0.1.0"
-unsigned-varint = { version = "0.2", features = ["codec"] }
+unsigned-varint = { version = "0.2.1", features = ["codec"] }
 
 [dev-dependencies]
 libp2p-tcp-transport = { path = "../../transports/tcp" }
diff --git a/protocols/identify/src/identify_transport.rs b/protocols/identify/src/identify_transport.rs
index bee1d5bb..dc039c0d 100644
--- a/protocols/identify/src/identify_transport.rs
+++ b/protocols/identify/src/identify_transport.rs
@@ -48,7 +48,7 @@ impl<Trans> Clone for IdentifyTransport<Trans>
     }
 }
 
-type CacheEntry = future::Shared<Box<Future<Item = IdentifyTransportOutcome, Error = IoError>>>;
+type CacheEntry = future::Shared<Box<Future<Item = IdentifyTransportOutcome, Error = IoError> + Send>>;
 
 impl<Trans> IdentifyTransport<Trans> {
     /// Creates an `IdentifyTransport` that wraps around the given transport and peerstore.
@@ -63,14 +63,18 @@ impl<Trans> IdentifyTransport<Trans> {
 
 impl<Trans> Transport for IdentifyTransport<Trans>
 where
-    Trans: Transport + Clone + 'static, // TODO: 'static :(
-    Trans::Output: AsyncRead + AsyncWrite,
+    Trans: Transport + Clone + Send + 'static, // TODO: 'static :(
+    Trans::Dial: Send,
+    Trans::Listener: Send,
+    Trans::ListenerUpgrade: Send,
+    Trans::MultiaddrFuture: Send,
+    Trans::Output: AsyncRead + AsyncWrite + Send,
 {
     type Output = IdentifyTransportOutput<Trans::Output>;
     type MultiaddrFuture = future::FutureResult<Multiaddr, IoError>;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
+    type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
@@ -139,7 +143,7 @@ where
                     Ok((out, future::ok(client_addr)))
                 });
 
-                Box::new(fut) as Box<Future<Item = _, Error = _>>
+                Box::new(fut) as Box<Future<Item = _, Error = _> + Send>
             });
 
         Ok((Box::new(listener) as Box<_>, new_addr))
@@ -213,11 +217,17 @@ where
 
 impl<Trans> MuxedTransport for IdentifyTransport<Trans>
 where
-    Trans: MuxedTransport + Clone + 'static,
-    Trans::Output: AsyncRead + AsyncWrite,
+    Trans: MuxedTransport + Clone + Send + 'static,
+    Trans::Dial: Send,
+    Trans::Listener: Send,
+    Trans::ListenerUpgrade: Send,
+    Trans::MultiaddrFuture: Send,
+    Trans::Output: AsyncRead + AsyncWrite + Send,
+    Trans::Incoming: Send,
+    Trans::IncomingUpgrade: Send,
 {
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError> + Send>;
+    type IncomingUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn next_incoming(self) -> Self::Incoming {
@@ -274,7 +284,7 @@ where
                     Ok((out, future::ok(client_addr)))
                 });
 
-            Box::new(future) as Box<Future<Item = _, Error = _>>
+            Box::new(future) as Box<Future<Item = _, Error = _> + Send>
         });
 
         Box::new(future) as Box<_>
@@ -286,7 +296,7 @@ pub struct IdentifyTransportOutput<S> {
     /// The socket to communicate with the remote.
     pub socket: S,
     /// Outcome of the identification of the remote.
-    pub info: Box<Future<Item = IdentifyTransportOutcome, Error = IoError>>,
+    pub info: Box<Future<Item = IdentifyTransportOutcome, Error = IoError> + Send>,
 }
 
 /// Outcome of the identification of the remote.
@@ -301,7 +311,7 @@ pub struct IdentifyTransportOutcome {
 fn cache_entry<F, Fut>(cache: &Mutex<FnvHashMap<Multiaddr, CacheEntry>>, addr: Multiaddr, if_no_entry: F)
     -> impl Future<Item = IdentifyTransportOutcome, Error = IoError>
 where F: FnOnce() -> Fut,
-      Fut: Future<Item = IdentifyTransportOutcome, Error = IoError> + 'static,
+      Fut: Future<Item = IdentifyTransportOutcome, Error = IoError> + Send + 'static,
 {
     trace!("Looking up cache entry for {}", addr);
     let mut cache = cache.lock();
@@ -313,7 +323,7 @@ where F: FnOnce() -> Fut,
 
         Entry::Vacant(entry) => {
             trace!("No cache entry available");
-            let future = (Box::new(if_no_entry()) as Box<Future<Item = _, Error = _>>).shared();
+            let future = (Box::new(if_no_entry()) as Box<Future<Item = _, Error = _> + Send>).shared();
             entry.insert(future.clone());
             future::Either::B(future)
         },
diff --git a/protocols/identify/src/peer_id_transport.rs b/protocols/identify/src/peer_id_transport.rs
index e96a2dd3..1d1d3536 100644
--- a/protocols/identify/src/peer_id_transport.rs
+++ b/protocols/identify/src/peer_id_transport.rs
@@ -45,16 +45,21 @@ impl<Trans, AddrRes> PeerIdTransport<Trans, AddrRes> {
 
 impl<Trans, AddrRes, AddrResOut> Transport for PeerIdTransport<Trans, AddrRes>
 where
-    Trans: Transport + Clone + 'static, // TODO: 'static :(
-    Trans::Output: AsyncRead + AsyncWrite,
+    Trans: Transport + Clone + Send + 'static, // TODO: 'static :(
+    Trans::Dial: Send,
+    Trans::Listener: Send,
+    Trans::ListenerUpgrade: Send,
+    Trans::MultiaddrFuture: Send,
+    Trans::Output: AsyncRead + AsyncWrite + Send,
     AddrRes: Fn(PeerId) -> AddrResOut + 'static,       // TODO: 'static :(
     AddrResOut: IntoIterator<Item = Multiaddr> + 'static,       // TODO: 'static :(
+    AddrResOut::IntoIter: Send,
 {
     type Output = PeerIdTransportOutput<Trans::Output>;
-    type MultiaddrFuture = Box<Future<Item = Multiaddr, Error = IoError>>;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-    type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type MultiaddrFuture = Box<Future<Item = Multiaddr, Error = IoError> + Send>;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
+    type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
@@ -94,11 +99,11 @@ where
                             let peer_id = info.info.public_key.clone().into_peer_id();
                             debug!("Identified {} as {:?}", original_addr, peer_id);
                             AddrComponent::P2P(peer_id.into()).into()
-                        })) as Box<Future<Item = _, Error = _>>;
+                        })) as Box<Future<Item = _, Error = _> + Send>;
                     (out, real_addr)
                 });
 
-            Box::new(fut) as Box<Future<Item = _, Error = _>>
+            Box::new(fut) as Box<Future<Item = _, Error = _> + Send>
         });
 
         Ok((Box::new(listener) as Box<_>, listened_addr))
@@ -155,7 +160,7 @@ where
                             original_addr: original_addr,
                         };
                         // Replace the multiaddress with the one of the form `/p2p/...` or `/ipfs/...`.
-                        Ok((out, Box::new(future::ok(addr)) as Box<Future<Item = _, Error = _>>))
+                        Ok((out, Box::new(future::ok(addr)) as Box<Future<Item = _, Error = _> + Send>))
                     });
 
                 Ok(Box::new(future) as Box<_>)
@@ -195,7 +200,7 @@ where
                                 let peer_id = info.info.public_key.clone().into_peer_id();
                                 debug!("Identified {} as {:?}", original_addr, peer_id);
                                 AddrComponent::P2P(peer_id.into()).into()
-                            })) as Box<Future<Item = _, Error = _>>;
+                            })) as Box<Future<Item = _, Error = _> + Send>;
                         (out, real_addr)
                     });
 
@@ -212,13 +217,20 @@ where
 
 impl<Trans, AddrRes, AddrResOut> MuxedTransport for PeerIdTransport<Trans, AddrRes>
 where
-    Trans: MuxedTransport + Clone + 'static,
-    Trans::Output: AsyncRead + AsyncWrite,
+    Trans: MuxedTransport + Clone + Send + 'static,
+    Trans::Dial: Send,
+    Trans::Listener: Send,
+    Trans::ListenerUpgrade: Send,
+    Trans::MultiaddrFuture: Send,
+    Trans::Output: AsyncRead + AsyncWrite + Send,
+    Trans::Incoming: Send,
+    Trans::IncomingUpgrade: Send,
     AddrRes: Fn(PeerId) -> AddrResOut + 'static,       // TODO: 'static :(
     AddrResOut: IntoIterator<Item = Multiaddr> + 'static,   // TODO: 'static :(
+    AddrResOut::IntoIter: Send,
 {
-    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
-    type IncomingUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError> + Send>;
+    type IncomingUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn next_incoming(self) -> Self::Incoming {
@@ -243,11 +255,11 @@ where
                             let peer_id = info.info.public_key.clone().into_peer_id();
                             debug!("Identified {} as {:?}", original_addr, peer_id);
                             AddrComponent::P2P(peer_id.into()).into()
-                        })) as Box<Future<Item = _, Error = _>>;
+                        })) as Box<Future<Item = _, Error = _> + Send>;
                     (out, real_addr)
                 });
 
-            Box::new(future) as Box<Future<Item = _, Error = _>>
+            Box::new(future) as Box<Future<Item = _, Error = _> + Send>
         });
 
         Box::new(future) as Box<_>
@@ -261,7 +273,7 @@ pub struct PeerIdTransportOutput<S> {
 
     /// Identification of the remote.
     /// This may not be known immediately, hence why we use a future.
-    pub info: Box<Future<Item = IdentifyTransportOutcome, Error = IoError>>,
+    pub info: Box<Future<Item = IdentifyTransportOutcome, Error = IoError> + Send>,
 
     /// Original address of the remote.
     /// This layer turns the address of the remote into the `/p2p/...` form, but stores the
@@ -313,8 +325,8 @@ mod tests {
         impl Transport for UnderlyingTrans {
             type Output = <TcpConfig as Transport>::Output;
             type MultiaddrFuture = <TcpConfig as Transport>::MultiaddrFuture;
-            type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
-            type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+            type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>;
+            type ListenerUpgrade = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
             type Dial = <TcpConfig as Transport>::Dial;
             #[inline]
             fn listen_on(
diff --git a/protocols/identify/src/protocol.rs b/protocols/identify/src/protocol.rs
index 0ed2bab2..31506a02 100644
--- a/protocols/identify/src/protocol.rs
+++ b/protocols/identify/src/protocol.rs
@@ -61,7 +61,7 @@ pub struct IdentifySender<T> {
 
 impl<'a, T> IdentifySender<T>
 where
-    T: AsyncWrite + 'a,
+    T: AsyncWrite + Send + 'a,
 {
     /// Sends back information to the client. Returns a future that is signalled whenever the
     /// info have been sent.
@@ -69,7 +69,7 @@ where
         self,
         info: IdentifyInfo,
         observed_addr: &Multiaddr,
-    ) -> Box<Future<Item = (), Error = IoError> + 'a> {
+    ) -> Box<Future<Item = (), Error = IoError> + Send + 'a> {
         debug!("Sending identify info to client");
         trace!("Sending: {:?}", info);
 
@@ -113,14 +113,14 @@ pub struct IdentifyInfo {
 
 impl<C, Maf> ConnectionUpgrade<C, Maf> for IdentifyProtocolConfig
 where
-    C: AsyncRead + AsyncWrite + 'static,
-    Maf: Future<Item = Multiaddr, Error = IoError> + 'static,
+    C: AsyncRead + AsyncWrite + Send + 'static,
+    Maf: Future<Item = Multiaddr, Error = IoError> + Send + 'static,
 {
     type NamesIter = iter::Once<(Bytes, Self::UpgradeIdentifier)>;
     type UpgradeIdentifier = ();
     type Output = IdentifyOutput<C>;
     type MultiaddrFuture = future::Either<future::FutureResult<Multiaddr, IoError>, Maf>;
-    type Future = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Future = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn protocol_names(&self) -> Self::NamesIter {
diff --git a/protocols/kad/Cargo.toml b/protocols/kad/Cargo.toml
index 8f38f9ca..e733f5e6 100644
--- a/protocols/kad/Cargo.toml
+++ b/protocols/kad/Cargo.toml
@@ -24,7 +24,7 @@ smallvec = "0.5"
 tokio-codec = "0.1"
 tokio-io = "0.1"
 tokio-timer = "0.2.6"
-unsigned-varint = { version = "0.2", features = ["codec"] }
+unsigned-varint = { version = "0.2.1", features = ["codec"] }
 
 [dev-dependencies]
 libp2p-tcp-transport = { path = "../../transports/tcp" }
diff --git a/protocols/kad/src/high_level.rs b/protocols/kad/src/high_level.rs
index 90e8c430..d838ed6d 100644
--- a/protocols/kad/src/high_level.rs
+++ b/protocols/kad/src/high_level.rs
@@ -76,8 +76,9 @@ impl KadSystem {
     /// This future should be driven to completion by the caller.
     pub fn start<'a, F, Fut>(config: KadSystemConfig<impl Iterator<Item = PeerId>>, access: F)
         -> (KadSystem, impl Future<Item = (), Error = IoError> + 'a)
-        where F: FnMut(&PeerId) -> Fut + Clone + 'a,
-            Fut: IntoFuture<Item = KadConnecController, Error = IoError>  + 'a,
+        where F: FnMut(&PeerId) -> Fut + Send + Clone + 'a,
+            Fut: IntoFuture<Item = KadConnecController, Error = IoError> + 'a,
+            Fut::Future: Send,
     {
         let system = KadSystem::without_init(config);
         let init_future = system.perform_initialization(access);
@@ -102,8 +103,9 @@ impl KadSystem {
 
     /// Starts an initialization process.
     pub fn perform_initialization<'a, F, Fut>(&self, access: F) -> impl Future<Item = (), Error = IoError> + 'a
-        where F: FnMut(&PeerId) -> Fut + Clone + 'a,
+        where F: FnMut(&PeerId) -> Fut + Send + Clone + 'a,
             Fut: IntoFuture<Item = KadConnecController, Error = IoError>  + 'a,
+            Fut::Future: Send,
     {
         let futures: Vec<_> = (0..256)      // TODO: 256 is arbitrary
             .map(|n| {
@@ -147,8 +149,9 @@ impl KadSystem {
     /// Starts a query for an iterative `FIND_NODE` request.
     pub fn find_node<'a, F, Fut>(&self, searched_key: PeerId, access: F)
         -> impl Stream<Item = KadQueryEvent<Vec<PeerId>>, Error = IoError> + 'a
-    where F: FnMut(&PeerId) -> Fut + 'a,
+    where F: FnMut(&PeerId) -> Fut + Send + 'a,
         Fut: IntoFuture<Item = KadConnecController, Error = IoError>  + 'a,
+        Fut::Future: Send,
     {
         query(access, &self.kbuckets, searched_key, self.parallelism as usize,
               20, self.request_timeout)  // TODO: arbitrary const
@@ -162,14 +165,15 @@ impl KadSystem {
 fn refresh<'a, F, Fut>(bucket_num: usize, access: F, kbuckets: &KBucketsTable<PeerId, ()>,
                         parallelism: usize, request_timeout: Duration)
     -> impl Stream<Item = KadQueryEvent<()>, Error = IoError> + 'a
-where F: FnMut(&PeerId) -> Fut + 'a,
+where F: FnMut(&PeerId) -> Fut + Send + 'a,
     Fut: IntoFuture<Item = KadConnecController, Error = IoError> + 'a,
+    Fut::Future: Send,
 {
     let peer_id = match gen_random_id(kbuckets.my_id(), bucket_num) {
         Ok(p) => p,
         Err(()) => {
             let stream = stream::once(Ok(KadQueryEvent::Finished(())));
-            return Box::new(stream) as Box<Stream<Item = _, Error = _>>;
+            return Box::new(stream) as Box<Stream<Item = _, Error = _> + Send>;
         },
     };
 
@@ -180,7 +184,7 @@ where F: FnMut(&PeerId) -> Fut + 'a,
                 KadQueryEvent::Finished(_) => KadQueryEvent::Finished(()),
             }
         });
-    Box::new(stream) as Box<Stream<Item = _, Error = _>>
+    Box::new(stream) as Box<Stream<Item = _, Error = _> + Send>
 }
 
 // Generates a random `PeerId` that belongs to the given bucket.
@@ -227,6 +231,7 @@ fn query<'a, F, Fut>(
 ) -> impl Stream<Item = KadQueryEvent<Vec<PeerId>>, Error = IoError> + 'a
 where F: FnMut(&PeerId) -> Fut + 'a,
       Fut: IntoFuture<Item = KadConnecController, Error = IoError> + 'a,
+      Fut::Future: Send,
 {
     debug!("Start query for {:?} ; num results = {}", searched_key, num_results);
 
@@ -240,7 +245,7 @@ where F: FnMut(&PeerId) -> Fut + 'a,
         result: Vec<PeerId>,
         // For each open connection, a future with the response of the remote.
         // Note that don't use a `SmallVec` here because `select_all` produces a `Vec`.
-        current_attempts_fut: Vec<Box<Future<Item = Vec<protocol::KadPeer>, Error = IoError> + 'a>>,
+        current_attempts_fut: Vec<Box<Future<Item = Vec<protocol::KadPeer>, Error = IoError> + Send + 'a>>,
         // For each open connection, the peer ID that we are connected to.
         // Must always have the same length as `current_attempts_fut`.
         current_attempts_addrs: SmallVec<[PeerId; 32]>,
diff --git a/protocols/kad/src/kad_server.rs b/protocols/kad/src/kad_server.rs
index 3f3343b4..d00a264d 100644
--- a/protocols/kad/src/kad_server.rs
+++ b/protocols/kad/src/kad_server.rs
@@ -65,11 +65,11 @@ impl KadConnecConfig {
 
 impl<C, Maf> ConnectionUpgrade<C, Maf> for KadConnecConfig
 where
-    C: AsyncRead + AsyncWrite + 'static, // TODO: 'static :-/
+    C: AsyncRead + AsyncWrite + Send + 'static, // TODO: 'static :-/
 {
     type Output = (
         KadConnecController,
-        Box<Stream<Item = KadIncomingRequest, Error = IoError>>,
+        Box<Stream<Item = KadIncomingRequest, Error = IoError> + Send>,
     );
     type MultiaddrFuture = Maf;
     type Future = future::Map<<KademliaProtocolConfig as ConnectionUpgrade<C, Maf>>::Future, fn((<KademliaProtocolConfig as ConnectionUpgrade<C, Maf>>::Output, Maf)) -> (Self::Output, Maf)>;
@@ -191,8 +191,8 @@ impl KadFindNodeRespond {
 }
 
 // Builds a controller and stream from a stream/sink of raw messages.
-fn build_from_sink_stream<'a, S>(connec: S) -> (KadConnecController, Box<Stream<Item = KadIncomingRequest, Error = IoError> + 'a>)
-where S: Sink<SinkItem = KadMsg, SinkError = IoError> + Stream<Item = KadMsg, Error = IoError> + 'a
+fn build_from_sink_stream<'a, S>(connec: S) -> (KadConnecController, Box<Stream<Item = KadIncomingRequest, Error = IoError> + Send + 'a>)
+where S: Sink<SinkItem = KadMsg, SinkError = IoError> + Stream<Item = KadMsg, Error = IoError> + Send + 'a
 {
     let (tx, rx) = mpsc::unbounded();
     let future = kademlia_handler(connec, rx);
@@ -211,9 +211,9 @@ where S: Sink<SinkItem = KadMsg, SinkError = IoError> + Stream<Item = KadMsg, Er
 fn kademlia_handler<'a, S>(
     kad_bistream: S,
     rq_rx: mpsc::UnboundedReceiver<(KadMsg, oneshot::Sender<KadMsg>)>,
-) -> Box<Stream<Item = KadIncomingRequest, Error = IoError> + 'a>
+) -> Box<Stream<Item = KadIncomingRequest, Error = IoError> + Send + 'a>
 where
-    S: Stream<Item = KadMsg, Error = IoError> + Sink<SinkItem = KadMsg, SinkError = IoError> + 'a,
+    S: Stream<Item = KadMsg, Error = IoError> + Sink<SinkItem = KadMsg, SinkError = IoError> + Send + 'a,
 {
     let (kad_sink, kad_stream) = kad_bistream.split();
 
@@ -255,7 +255,7 @@ where
             Some(events
                 .into_future()
                 .map_err(|(err, _)| err)
-                .and_then(move |(message, events)| -> Box<Future<Item = _, Error = _>> {
+                .and_then(move |(message, events)| -> Box<Future<Item = _, Error = _> + Send> {
                     match message {
                         Some(EventSource::Finished) | None => {
                             let future = future::ok({
@@ -397,7 +397,7 @@ where
                 }))
     }).filter_map(|val| val);
 
-    Box::new(stream) as Box<Stream<Item = _, Error = IoError>>
+    Box::new(stream) as Box<Stream<Item = _, Error = IoError> + Send>
 }
 
 #[cfg(test)]
diff --git a/protocols/kad/src/query.rs b/protocols/kad/src/query.rs
index 6098a63c..fec81e5c 100644
--- a/protocols/kad/src/query.rs
+++ b/protocols/kad/src/query.rs
@@ -59,10 +59,10 @@ pub enum QueryEvent<TOut> {
 pub fn find_node<'a, FBuckets, FFindNode>(
     query_params: QueryParams<FBuckets, FFindNode>,
     searched_key: PeerId,
-) -> Box<Stream<Item = QueryEvent<Vec<PeerId>>, Error = IoError> + 'a>
+) -> Box<Stream<Item = QueryEvent<Vec<PeerId>>, Error = IoError> + Send + 'a>
 where
     FBuckets: Fn(PeerId) -> Vec<PeerId> + 'a + Clone,
-    FFindNode: Fn(Multiaddr, PeerId) -> Box<Future<Item = Vec<protocol::Peer>, Error = IoError>> + 'a + Clone,
+    FFindNode: Fn(Multiaddr, PeerId) -> Box<Future<Item = Vec<protocol::Peer>, Error = IoError> + Send> + 'a + Clone,
 {
     query(query_params, searched_key, 20) // TODO: constant
 }
@@ -74,10 +74,10 @@ where
 pub fn refresh<'a, FBuckets, FFindNode>(
     query_params: QueryParams<FBuckets, FFindNode>,
     bucket_num: usize,
-) -> Box<Stream<Item = QueryEvent<()>, Error = IoError> + 'a>
+) -> Box<Stream<Item = QueryEvent<()>, Error = IoError> + Send + 'a>
 where
     FBuckets: Fn(PeerId) -> Vec<PeerId> + 'a + Clone,
-    FFindNode: Fn(Multiaddr, PeerId) -> Box<Future<Item = Vec<protocol::Peer>, Error = IoError>> + 'a + Clone,
+    FFindNode: Fn(Multiaddr, PeerId) -> Box<Future<Item = Vec<protocol::Peer>, Error = IoError> + Send> + 'a + Clone,
 {
     let peer_id = match gen_random_id(&query_params.local_id, bucket_num) {
         Ok(p) => p,
@@ -132,10 +132,10 @@ fn query<'a, FBuckets, FFindNode>(
     query_params: QueryParams<FBuckets, FFindNode>,
     searched_key: PeerId,
     num_results: usize,
-) -> Box<Stream<Item = QueryEvent<Vec<PeerId>>, Error = IoError> + 'a>
+) -> Box<Stream<Item = QueryEvent<Vec<PeerId>>, Error = IoError> + Send + 'a>
 where
     FBuckets: Fn(PeerId) -> Vec<PeerId> + 'a + Clone,
-    FFindNode: Fn(Multiaddr, PeerId) -> Box<Future<Item = Vec<protocol::Peer>, Error = IoError>> + 'a + Clone,
+    FFindNode: Fn(Multiaddr, PeerId) -> Box<Future<Item = Vec<protocol::Peer>, Error = IoError> + Send> + 'a + Clone,
 {
     debug!("Start query for {:?} ; num results = {}", searched_key, num_results);
 
@@ -147,7 +147,7 @@ where
         result: Vec<PeerId>,
         // For each open connection, a future with the response of the remote.
         // Note that don't use a `SmallVec` here because `select_all` produces a `Vec`.
-        current_attempts_fut: Vec<Box<Future<Item = Vec<protocol::Peer>, Error = IoError> + 'a>>,
+        current_attempts_fut: Vec<Box<Future<Item = Vec<protocol::Peer>, Error = IoError> + Send + 'a>>,
         // For each open connection, the peer ID that we are connected to.
         // Must always have the same length as `current_attempts_fut`.
         current_attempts_addrs: SmallVec<[PeerId; 32]>,
diff --git a/protocols/ping/src/lib.rs b/protocols/ping/src/lib.rs
index adcd4e99..a9cec286 100644
--- a/protocols/ping/src/lib.rs
+++ b/protocols/ping/src/lib.rs
@@ -65,10 +65,10 @@
 //!     .dial("127.0.0.1:12345".parse::<libp2p_core::Multiaddr>().unwrap()).unwrap_or_else(|_| panic!())
 //!     .and_then(|(out, _)| {
 //!         match out {
-//!             PingOutput::Ponger(processing) => Box::new(processing) as Box<Future<Item = _, Error = _>>,
+//!             PingOutput::Ponger(processing) => Box::new(processing) as Box<Future<Item = _, Error = _> + Send>,
 //!             PingOutput::Pinger { mut pinger, processing } => {
 //!                 let f = pinger.ping().map_err(|_| panic!()).select(processing).map(|_| ()).map_err(|(err, _)| err);
-//!                 Box::new(f) as Box<Future<Item = _, Error = _>>
+//!                 Box::new(f) as Box<Future<Item = _, Error = _> + Send>
 //!             },
 //!         }
 //!     });
@@ -118,15 +118,15 @@ pub enum PingOutput {
         /// Object to use in order to ping the remote.
         pinger: Pinger,
         /// Future that drives the processing of the pings.
-        processing: Box<Future<Item = (), Error = IoError>>,
+        processing: Box<Future<Item = (), Error = IoError> + Send>,
     },
     /// We are on the listening side.
-    Ponger(Box<Future<Item = (), Error = IoError>>),
+    Ponger(Box<Future<Item = (), Error = IoError> + Send>),
 }
 
 impl<C, Maf> ConnectionUpgrade<C, Maf> for Ping
 where
-    C: AsyncRead + AsyncWrite + 'static,
+    C: AsyncRead + AsyncWrite + Send + 'static,
 {
     type NamesIter = iter::Once<(Bytes, Self::UpgradeIdentifier)>;
     type UpgradeIdentifier = ();
@@ -158,7 +158,7 @@ where
 }
 
 /// Upgrades a connection from the dialer side.
-fn upgrade_as_dialer(socket: impl AsyncRead + AsyncWrite + 'static) -> PingOutput {
+fn upgrade_as_dialer(socket: impl AsyncRead + AsyncWrite + Send + 'static) -> PingOutput {
     // # How does it work?
     //
     // All the actual processing is performed by the *ponger*.
@@ -199,7 +199,7 @@ fn upgrade_as_dialer(socket: impl AsyncRead + AsyncWrite + 'static) -> PingOutpu
                             Box::new(
                                 sink.send(payload)
                                     .map(|sink| Loop::Continue((sink, stream))),
-                            ) as Box<Future<Item = _, Error = _>>
+                            ) as Box<Future<Item = _, Error = _> + Send>
                         }
                         Message::Received(payload) => {
                             // Received a payload from the remote.
@@ -210,17 +210,17 @@ fn upgrade_as_dialer(socket: impl AsyncRead + AsyncWrite + 'static) -> PingOutpu
                                 debug!("Received pong (payload={:?}) ; ping fufilled", payload);
                                 let _ = fut.send(());
                                 Box::new(Ok(Loop::Continue((sink, stream))).into_future())
-                                    as Box<Future<Item = _, Error = _>>
+                                    as Box<Future<Item = _, Error = _> + Send>
                             } else {
                                 // Payload was unexpected. Closing connection.
                                 debug!("Received invalid payload ({:?}) ; closing", payload);
                                 Box::new(Ok(Loop::Break(())).into_future())
-                                    as Box<Future<Item = _, Error = _>>
+                                    as Box<Future<Item = _, Error = _> + Send>
                             }
                         }
                     }
                 } else {
-                    Box::new(Ok(Loop::Break(())).into_future()) as Box<Future<Item = _, Error = _>>
+                    Box::new(Ok(Loop::Break(())).into_future()) as Box<Future<Item = _, Error = _> + Send>
                 }
             })
     });
@@ -232,7 +232,7 @@ fn upgrade_as_dialer(socket: impl AsyncRead + AsyncWrite + 'static) -> PingOutpu
 }
 
 /// Upgrades a connection from the listener side.
-fn upgrade_as_listener(socket: impl AsyncRead + AsyncWrite + 'static) -> PingOutput {
+fn upgrade_as_listener(socket: impl AsyncRead + AsyncWrite + Send + 'static) -> PingOutput {
     let sink_stream = Framed::new(socket, Codec);
     let (sink, stream) = sink_stream.split();
 
@@ -247,10 +247,10 @@ fn upgrade_as_listener(socket: impl AsyncRead + AsyncWrite + 'static) -> PingOut
                     Box::new(
                         sink.send(payload.freeze())
                             .map(|sink| Loop::Continue((sink, stream))),
-                    ) as Box<Future<Item = _, Error = _>>
+                    ) as Box<Future<Item = _, Error = _> + Send>
                 } else {
                     // Connection was closed
-                    Box::new(Ok(Loop::Break(())).into_future()) as Box<Future<Item = _, Error = _>>
+                    Box::new(Ok(Loop::Break(())).into_future()) as Box<Future<Item = _, Error = _> + Send>
                 }
             })
     });
@@ -269,7 +269,7 @@ impl Pinger {
     ///
     /// **Note**: Please be aware that there is no timeout on the ping. You should handle the
     ///           timeout yourself when you call this function.
-    pub fn ping(&mut self) -> Box<Future<Item = (), Error = Box<Error + Send + Sync>>> {
+    pub fn ping(&mut self) -> Box<Future<Item = (), Error = Box<Error + Send + Sync>> + Send> {
         let (tx, rx) = oneshot::channel();
 
         let payload: [u8; 32] = self.rng.sample(Standard);
diff --git a/protocols/secio/src/handshake.rs b/protocols/secio/src/handshake.rs
index 7c98f72e..c7da0143 100644
--- a/protocols/secio/src/handshake.rs
+++ b/protocols/secio/src/handshake.rs
@@ -59,9 +59,9 @@ use {SecioKeyPair, SecioKeyPairInner};
 pub fn handshake<'a, S: 'a>(
     socket: S,
     local_key: SecioKeyPair,
-) -> Box<Future<Item = (FullCodec<S>, PublicKey, Vec<u8>), Error = SecioError> + 'a>
+) -> Box<Future<Item = (FullCodec<S>, PublicKey, Vec<u8>), Error = SecioError> + Send + 'a>
 where
-    S: AsyncRead + AsyncWrite,
+    S: AsyncRead + AsyncWrite + Send,
 {
     // TODO: could be rewritten as a coroutine once coroutines land in stable Rust
 
diff --git a/protocols/secio/src/lib.rs b/protocols/secio/src/lib.rs
index c8452e52..0f88f94e 100644
--- a/protocols/secio/src/lib.rs
+++ b/protocols/secio/src/lib.rs
@@ -289,12 +289,12 @@ where
 
 impl<S, Maf> libp2p_core::ConnectionUpgrade<S, Maf> for SecioConfig
 where
-    S: AsyncRead + AsyncWrite + 'static, // TODO: 'static :(
-    Maf: 'static,                        // TODO: 'static :(
+    S: AsyncRead + AsyncWrite + Send + 'static, // TODO: 'static :(
+    Maf: Send + 'static,                        // TODO: 'static :(
 {
     type Output = SecioOutput<S>;
     type MultiaddrFuture = Maf;
-    type Future = Box<Future<Item = (Self::Output, Maf), Error = IoError>>;
+    type Future = Box<Future<Item = (Self::Output, Maf), Error = IoError> + Send>;
     type NamesIter = iter::Once<(Bytes, ())>;
     type UpgradeIdentifier = ();
 
@@ -342,7 +342,7 @@ pub struct SecioMiddleware<S> {
 
 impl<S> SecioMiddleware<S>
 where
-    S: AsyncRead + AsyncWrite,
+    S: AsyncRead + AsyncWrite + Send,
 {
     /// Attempts to perform a handshake on the given socket.
     ///
@@ -351,7 +351,7 @@ where
     pub fn handshake<'a>(
         socket: S,
         key_pair: SecioKeyPair,
-    ) -> Box<Future<Item = (SecioMiddleware<S>, PublicKey, Vec<u8>), Error = SecioError> + 'a>
+    ) -> Box<Future<Item = (SecioMiddleware<S>, PublicKey, Vec<u8>), Error = SecioError> + Send + 'a>
     where
         S: 'a,
     {
diff --git a/src/simple.rs b/src/simple.rs
index 5cebe43e..f640af86 100644
--- a/src/simple.rs
+++ b/src/simple.rs
@@ -62,8 +62,8 @@ where
     C: AsyncRead + AsyncWrite,
     F: Fn(C) -> O,
     O: IntoFuture<Error = IoError>,
-    O::Future: 'static,
-    Maf: 'static,
+    O::Future: Send + 'static,
+    Maf: Send + 'static,
 {
     type NamesIter = iter::Once<(Bytes, ())>;
     type UpgradeIdentifier = ();
@@ -75,7 +75,7 @@ where
 
     type Output = O::Item;
     type MultiaddrFuture = Maf;
-    type Future = Box<Future<Item = (O::Item, Self::MultiaddrFuture), Error = IoError>>;
+    type Future = Box<Future<Item = (O::Item, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn upgrade(self, socket: C, _: (), _: Endpoint, client_addr: Maf) -> Self::Future {
diff --git a/transports/dns/src/lib.rs b/transports/dns/src/lib.rs
index 24e7d4e9..cdff70b0 100644
--- a/transports/dns/src/lib.rs
+++ b/transports/dns/src/lib.rs
@@ -94,13 +94,14 @@ where
 
 impl<T> Transport for DnsConfig<T>
 where
-    T: Transport + 'static, // TODO: 'static :-/
+    T: Transport + Send + 'static, // TODO: 'static :-/
+    T::Dial: Send,
 {
     type Output = T::Output;
     type MultiaddrFuture = T::MultiaddrFuture;
     type Listener = T::Listener;
     type ListenerUpgrade = T::ListenerUpgrade;
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
diff --git a/transports/ratelimit/src/lib.rs b/transports/ratelimit/src/lib.rs
index c5fa55a7..9fc86a24 100644
--- a/transports/ratelimit/src/lib.rs
+++ b/transports/ratelimit/src/lib.rs
@@ -157,13 +157,15 @@ where
 impl<T> Transport for RateLimited<T>
 where
     T: Transport + 'static,
-    T::Output: AsyncRead + AsyncWrite,
+    T::Dial: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: AsyncRead + AsyncWrite + Send,
 {
     type Output = Connection<T::Output>;
     type MultiaddrFuture = T::MultiaddrFuture;
     type Listener = Listener<T>;
     type ListenerUpgrade = ListenerUpgrade<T>;
-    type Dial = Box<Future<Item = (Connection<T::Output>, Self::MultiaddrFuture), Error = io::Error>>;
+    type Dial = Box<Future<Item = (Connection<T::Output>, Self::MultiaddrFuture), Error = io::Error> + Send>;
 
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)>
     where
diff --git a/transports/relay/Cargo.toml b/transports/relay/Cargo.toml
index edecf4cf..0fa426b2 100644
--- a/transports/relay/Cargo.toml
+++ b/transports/relay/Cargo.toml
@@ -15,4 +15,4 @@ protobuf = "2.0.2"
 rand = "0.4"
 tokio-codec = "0.1"
 tokio-io = "0.1"
-unsigned-varint = { version = "0.2", features = ["codec"] }
+unsigned-varint = { version = "0.2.1", features = ["codec"] }
diff --git a/transports/relay/src/protocol.rs b/transports/relay/src/protocol.rs
index fc8c5779..b08ba981 100644
--- a/transports/relay/src/protocol.rs
+++ b/transports/relay/src/protocol.rs
@@ -46,17 +46,21 @@ pub struct RelayConfig<T, P> {
 // but otherwise the stream is not programmatically accessible.
 pub enum Output<C> {
     Stream(C),
-    Sealed(Box<Future<Item=(), Error=io::Error>>)
+    Sealed(Box<Future<Item=(), Error=io::Error> + Send>)
 }
 
 impl<C, T, P, S, Maf> ConnectionUpgrade<C, Maf> for RelayConfig<T, P>
 where
-    C: AsyncRead + AsyncWrite + 'static,
-    T: Transport + Clone + 'static,
-    T::Output: AsyncRead + AsyncWrite,
-    P: Deref<Target=S> + Clone + 'static,
+    C: AsyncRead + AsyncWrite + Send + 'static,
+    T: Transport + Clone + Send + 'static,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: AsyncRead + AsyncWrite + Send,
+    P: Deref<Target=S> + Clone + Send + 'static,
     S: 'static,
-    Maf: 'static,
+    Maf: Send + 'static,
     for<'a> &'a S: Peerstore
 {
     type NamesIter = iter::Once<(Bytes, Self::UpgradeIdentifier)>;
@@ -68,7 +72,7 @@ where
 
     type Output = Output<C>;
     type MultiaddrFuture = Maf;
-    type Future = Box<Future<Item=(Self::Output, Maf), Error=io::Error>>;
+    type Future = Box<Future<Item=(Self::Output, Maf), Error=io::Error> + Send>;
 
     fn upgrade(self, conn: C, _: (), _: Endpoint, remote_addr: Maf) -> Self::Future {
         let future = Io::new(conn).recv().and_then(move |(message, io)| {
@@ -98,7 +102,11 @@ where
 impl<T, P, S> RelayConfig<T, P>
 where
     T: Transport + Clone + 'static,
-    T::Output: AsyncRead + AsyncWrite,
+    T::Dial: Send,      // TODO: remove
+    T::Listener: Send,      // TODO: remove
+    T::ListenerUpgrade: Send,      // TODO: remove
+    T::MultiaddrFuture: Send,      // TODO: remove
+    T::Output: Send + AsyncRead + AsyncWrite,
     P: Deref<Target = S> + Clone + 'static,
     for<'a> &'a S: Peerstore,
 {
@@ -268,8 +276,8 @@ pub(crate) struct Source(pub(crate) CircuitRelay);
 
 impl<C, Maf> ConnectionUpgrade<C, Maf> for Source
 where
-    C: AsyncRead + AsyncWrite + 'static,
-    Maf: 'static,
+    C: AsyncRead + AsyncWrite + Send + 'static,
+    Maf: Send + 'static,
 {
     type NamesIter = iter::Once<(Bytes, Self::UpgradeIdentifier)>;
     type UpgradeIdentifier = ();
@@ -280,7 +288,7 @@ where
 
     type Output = C;
     type MultiaddrFuture = Maf;
-    type Future = Box<Future<Item=(Self::Output, Maf), Error=io::Error>>;
+    type Future = Box<Future<Item=(Self::Output, Maf), Error=io::Error> + Send>;
 
     fn upgrade(self, conn: C, _: (), _: Endpoint, remote_addr: Maf) -> Self::Future {
         let future = Io::new(conn)
diff --git a/transports/relay/src/transport.rs b/transports/relay/src/transport.rs
index c3c85595..fe2c8b95 100644
--- a/transports/relay/src/transport.rs
+++ b/transports/relay/src/transport.rs
@@ -39,17 +39,21 @@ pub struct RelayTransport<T, P> {
 
 impl<T, P, S> Transport for RelayTransport<T, P>
 where
-    T: Transport + Clone + 'static,
-    T::Output: AsyncRead + AsyncWrite,
+    T: Transport + Send + Clone + 'static,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: AsyncRead + AsyncWrite + Send,
     P: Deref<Target=S> + Clone + 'static,
     S: 'static,
     for<'a> &'a S: Peerstore
 {
     type Output = T::Output;
     type MultiaddrFuture = T::MultiaddrFuture;
-    type Listener = Box<Stream<Item=Self::ListenerUpgrade, Error=io::Error>>;
-    type ListenerUpgrade = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error>>;
-    type Dial = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error>>;
+    type Listener = Box<Stream<Item=Self::ListenerUpgrade, Error=io::Error> + Send>;
+    type ListenerUpgrade = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error> + Send>;
+    type Dial = Box<Future<Item=(Self::Output, Self::MultiaddrFuture), Error=io::Error> + Send>;
 
     fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
         Err((self, addr))
@@ -85,7 +89,11 @@ where
 impl<T, P, S> RelayTransport<T, P>
 where
     T: Transport + Clone + 'static,
-    T::Output: AsyncRead + AsyncWrite,
+    T::Dial: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
+    T::MultiaddrFuture: Send,
+    T::Output: AsyncRead + AsyncWrite + Send,
     P: Deref<Target=S> + Clone + 'static,
     for<'a> &'a S: Peerstore
 {
diff --git a/transports/websocket/Cargo.toml b/transports/websocket/Cargo.toml
index 99e1927d..1a24209d 100644
--- a/transports/websocket/Cargo.toml
+++ b/transports/websocket/Cargo.toml
@@ -13,7 +13,9 @@ rw-stream-sink = { path = "../../misc/rw-stream-sink" }
 tokio-io = "0.1"
 
 [target.'cfg(not(target_os = "emscripten"))'.dependencies]
-websocket = { version = "0.20.2", default-features = false, features = ["async", "async-ssl"] }
+# TODO: restore the upstream version once the branch is merged
+websocket = { git = "https://github.com/tomaka/rust-websocket", branch = "send", default-features = false, features = ["async", "async-ssl"] }
+#websocket = { version = "0.20.2", default-features = false, features = ["async", "async-ssl"] }
 
 [target.'cfg(target_os = "emscripten")'.dependencies]
 stdweb = { version = "0.1.3", default-features = false }
diff --git a/transports/websocket/src/browser.rs b/transports/websocket/src/browser.rs
index 15f28629..3bae2b70 100644
--- a/transports/websocket/src/browser.rs
+++ b/transports/websocket/src/browser.rs
@@ -54,10 +54,10 @@ impl BrowserWsConfig {
 impl Transport for BrowserWsConfig {
     type Output = BrowserWsConn;
     type MultiaddrFuture = FutureResult<Multiaddr, IoError>;
-    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>; // TODO: use `!`
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError> + Send>; // TODO: use `!`
     type ListenerUpgrade =
-        Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>; // TODO: use `!`
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+        Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>; // TODO: use `!`
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     #[inline]
     fn listen_on(self, a: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
diff --git a/transports/websocket/src/desktop.rs b/transports/websocket/src/desktop.rs
index 9a741bf0..ece2943e 100644
--- a/transports/websocket/src/desktop.rs
+++ b/transports/websocket/src/desktop.rs
@@ -59,16 +59,20 @@ impl<T> Transport for WsConfig<T>
 where
     // TODO: this 'static is pretty arbitrary and is necessary because of the websocket library
     T: Transport + 'static,
+    T::Dial: Send,
+    T::MultiaddrFuture: Send,
+    T::Listener: Send,
+    T::ListenerUpgrade: Send,
     // TODO: this Send is pretty arbitrary and is necessary because of the websocket library
     T::Output: AsyncRead + AsyncWrite + Send,
 {
-    type Output = Box<AsyncStream>;
-    type MultiaddrFuture = Box<Future<Item = Multiaddr, Error = IoError>>;
+    type Output = Box<AsyncStream + Send>;
+    type MultiaddrFuture = Box<Future<Item = Multiaddr, Error = IoError> + Send>;
     type Listener =
         stream::Map<T::Listener, fn(<T as Transport>::ListenerUpgrade) -> Self::ListenerUpgrade>;
     type ListenerUpgrade =
-        Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
-    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+        Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError> + Send>;
 
     fn listen_on(
         self,
@@ -139,16 +143,16 @@ where
                                     .map(|v| v.expect("we only take while this is Some"));
 
                                 let read_write = RwStreamSink::new(framed_data);
-                                Box::new(read_write) as Box<AsyncStream>
+                                Box::new(read_write) as Box<AsyncStream + Send>
                             })
                     })
-                    .map(|s| Box::new(Ok(s).into_future()) as Box<Future<Item = _, Error = _>>)
+                    .map(|s| Box::new(Ok(s).into_future()) as Box<Future<Item = _, Error = _> + Send>)
                     .into_future()
                     .flatten()
-                    .map(move |v| (v, Box::new(client_addr) as Box<Future<Item = _, Error = _>>))
+                    .map(move |v| (v, Box::new(client_addr) as Box<Future<Item = _, Error = _> + Send>))
             });
 
-            Box::new(upgraded) as Box<Future<Item = _, Error = _>>
+            Box::new(upgraded) as Box<Future<Item = _, Error = _> + Send>
         });
 
         Ok((listen, new_addr))
@@ -198,7 +202,7 @@ where
                         addr.append(AddrComponent::WS);
                     };
                     addr
-                })) as Box<Future<Item = _, Error = _>>;
+                })) as Box<Future<Item = _, Error = _> + Send>;
 
                 ClientBuilder::new(&ws_addr)
                     .expect("generated ws address is always valid")
@@ -223,7 +227,7 @@ where
                                 }
                             });
                         let read_write = RwStreamSink::new(framed_data);
-                        Box::new(read_write) as Box<AsyncStream>
+                        Box::new(read_write) as Box<AsyncStream + Send>
                     })
                     .map(move |c| (c, client_addr))
             });