diff --git a/tokio-postgres/src/lib.rs b/tokio-postgres/src/lib.rs
index 5fdd9fce..27dd6614 100644
--- a/tokio-postgres/src/lib.rs
+++ b/tokio-postgres/src/lib.rs
@@ -99,7 +99,8 @@ impl Client {
 
     pub fn copy_in<S>(&mut self, statement: &Statement, params: &[&ToSql], stream: S) -> CopyIn<S>
     where
-        S: Stream<Item = Vec<u8>>,
+        S: Stream,
+        S::Item: AsRef<[u8]>,
         S::Error: Into<Box<StdError + Sync + Send>>,
     {
         CopyIn(self.0.copy_in(&statement.0, params, stream))
@@ -239,7 +240,8 @@ impl Stream for Query {
 #[must_use = "futures do nothing unless polled"]
 pub struct CopyIn<S>(proto::CopyInFuture<S>)
 where
-    S: Stream<Item = Vec<u8>>,
+    S: Stream,
+    S::Item: AsRef<[u8]>,
     S::Error: Into<Box<StdError + Sync + Send>>;
 
 impl<S> Future for CopyIn<S>
diff --git a/tokio-postgres/src/proto/client.rs b/tokio-postgres/src/proto/client.rs
index 4ceb922a..eca8956b 100644
--- a/tokio-postgres/src/proto/client.rs
+++ b/tokio-postgres/src/proto/client.rs
@@ -142,7 +142,8 @@ impl Client {
 
     pub fn copy_in<S>(&self, statement: &Statement, params: &[&ToSql], stream: S) -> CopyInFuture<S>
     where
-        S: Stream<Item = Vec<u8>>,
+        S: Stream,
+        S::Item: AsRef<[u8]>,
         S::Error: Into<Box<StdError + Sync + Send>>,
     {
         let (mut sender, receiver) = mpsc::channel(0);
diff --git a/tokio-postgres/src/proto/copy_in.rs b/tokio-postgres/src/proto/copy_in.rs
index 12fc69ab..cec324d2 100644
--- a/tokio-postgres/src/proto/copy_in.rs
+++ b/tokio-postgres/src/proto/copy_in.rs
@@ -63,7 +63,8 @@ impl Stream for CopyInReceiver {
 #[derive(StateMachineFuture)]
 pub enum CopyIn<S>
 where
-    S: Stream<Item = Vec<u8>>,
+    S: Stream,
+    S::Item: AsRef<[u8]>,
     S::Error: Into<Box<StdError + Sync + Send>>,
 {
     #[state_machine_future(start, transitions(ReadCopyInResponse))]
@@ -102,7 +103,8 @@ where
 
 impl<S> PollCopyIn<S> for CopyIn<S>
 where
-    S: Stream<Item = Vec<u8>>,
+    S: Stream,
+    S::Item: AsRef<[u8]>,
     S::Error: Into<Box<StdError + Sync + Send>>,
 {
     fn poll_start<'a>(state: &'a mut RentToOwn<'a, Start<S>>) -> Poll<AfterStart<S>, Error> {
@@ -150,7 +152,7 @@ where
                 None => match try_ready!(state.stream.poll().map_err(error::__user)) {
                     Some(data) => {
                         let mut buf = vec![];
-                        frontend::copy_data(&data, &mut buf).map_err(error::io)?;
+                        frontend::copy_data(data.as_ref(), &mut buf).map_err(error::io)?;
                         CopyMessage::Data(buf)
                     }
                     None => {
@@ -204,7 +206,8 @@ where
 
 impl<S> CopyInFuture<S>
 where
-    S: Stream<Item = Vec<u8>>,
+    S: Stream,
+    S::Item: AsRef<[u8]>,
     S::Error: Into<Box<StdError + Sync + Send>>,
 {
     pub fn new(