diff --git a/src/future/client.rs b/src/future/client.rs
index 7d1ae1b..85cf880 100644
--- a/src/future/client.rs
+++ b/src/future/client.rs
@@ -120,9 +120,9 @@ impl<Req, Resp, E> Clone for Client<Req, Resp, E>
 }
 
 impl<Req, Resp, E> Service for Client<Req, Resp, E>
-    where Req: Serialize + Sync + Send + 'static,
-          Resp: Deserialize + Sync + Send + 'static,
-          E: Deserialize + Sync + Send + 'static
+    where Req: Serialize + Send + 'static,
+          Resp: Deserialize + Send + 'static,
+          E: Deserialize + Send + 'static
 {
     type Request = Req;
     type Response = Resp;
@@ -147,9 +147,9 @@ impl<Req, Resp, E> Client<Req, Resp, E>
           E: Deserialize + 'static
 {
     fn bind(handle: &reactor::Handle, tcp: StreamType, max_payload_size: u64) -> Self
-        where Req: Serialize + Sync + Send + 'static,
-              Resp: Deserialize + Sync + Send + 'static,
-              E: Deserialize + Sync + Send + 'static
+        where Req: Serialize + Send + 'static,
+              Resp: Deserialize + Send + 'static,
+              E: Deserialize + Send + 'static
     {
         let inner = Proto::new(max_payload_size).bind_client(&handle, tcp);
         Client { inner }
@@ -187,9 +187,9 @@ pub type ConnectFuture<Req, Resp, E> =
                                      fn(futures::Canceled) -> io::Error>>;
 
 impl<Req, Resp, E> ClientExt for Client<Req, Resp, E>
-    where Req: Serialize + Sync + Send + 'static,
-          Resp: Deserialize + Sync + Send + 'static,
-          E: Deserialize + Sync + Send + 'static
+    where Req: Serialize + Send + 'static,
+          Resp: Deserialize + Send + 'static,
+          E: Deserialize + Send + 'static
 {
     type ConnectFut = ConnectFuture<Req, Resp, E>;
 
diff --git a/src/sync/client.rs b/src/sync/client.rs
index f56467b..4b84488 100644
--- a/src/sync/client.rs
+++ b/src/sync/client.rs
@@ -36,9 +36,9 @@ impl<Req, Resp, E> fmt::Debug for Client<Req, Resp, E> {
 }
 
 impl<Req, Resp, E> Client<Req, Resp, E>
-    where Req: Serialize + Sync + Send + 'static,
-          Resp: Deserialize + Sync + Send + 'static,
-          E: Deserialize + Sync + Send + 'static
+    where Req: Serialize + Send + 'static,
+          Resp: Deserialize + Send + 'static,
+          E: Deserialize + Send + 'static
 {
     /// Drives an RPC call for the given request.
     pub fn call(&self, request: Req) -> Result<Resp, ::Error<E>> {
@@ -128,9 +128,9 @@ pub trait ClientExt: Sized {
 }
 
 impl<Req, Resp, E> ClientExt for Client<Req, Resp, E>
-    where Req: Serialize + Sync + Send + 'static,
-          Resp: Deserialize + Sync + Send + 'static,
-          E: Deserialize + Sync + Send + 'static
+    where Req: Serialize + Send + 'static,
+          Resp: Deserialize + Send + 'static,
+          E: Deserialize + Send + 'static
 {
     fn connect<A>(addr: A, options: Options) -> io::Result<Self>
         where A: ToSocketAddrs
@@ -160,9 +160,9 @@ struct RequestHandler<Req, Resp, E, S> {
 }
 
 impl<Req, Resp, E> RequestHandler<Req, Resp, E, FutureClient<Req, Resp, E>>
-    where Req: Serialize + Sync + Send + 'static,
-          Resp: Deserialize + Sync + Send + 'static,
-          E: Deserialize + Sync + Send + 'static
+    where Req: Serialize + Send + 'static,
+          Resp: Deserialize + Send + 'static,
+          E: Deserialize + Send + 'static
 {
     /// Creates a new `RequestHandler` by connecting a `FutureClient` to the given address
     /// using the given options.