diff --git a/src/liballoc/arc.rs b/src/liballoc/arc.rs
index f87c450eda5e..8b884c56505b 100644
--- a/src/liballoc/arc.rs
+++ b/src/liballoc/arc.rs
@@ -321,7 +321,7 @@ impl<T> Deref for Arc<T> {
     }
 }
 
-impl<T: Send + Sync + Clone> Arc<T> {
+impl<T: Clone> Arc<T> {
     /// Make a mutable reference from the given `Arc<T>`.
     ///
     /// This is also referred to as a copy-on-write operation because the inner
@@ -465,7 +465,7 @@ impl<T> Weak<T> {
 
 #[unstable(feature = "alloc",
            reason = "Weak pointers may not belong in this module.")]
-impl<T: Sync + Send> Clone for Weak<T> {
+impl<T> Clone for Weak<T> {
     /// Makes a clone of the `Weak<T>`.
     ///
     /// This increases the weak reference count.
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index e14f32865fa1..b436e49feabb 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -488,7 +488,7 @@ impl<T:Send> UnsafeFlavor<T> for Receiver<T> {
 /// println!("{:?}", rx.recv().unwrap());
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
-pub fn channel<T: Send>() -> (Sender<T>, Receiver<T>) {
+pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
     let a = Arc::new(UnsafeCell::new(oneshot::Packet::new()));
     (Sender::new(Flavor::Oneshot(a.clone())), Receiver::new(Flavor::Oneshot(a)))
 }
@@ -528,7 +528,7 @@ pub fn channel<T: Send>() -> (Sender<T>, Receiver<T>) {
 /// assert_eq!(rx.recv().unwrap(), 2);
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
-pub fn sync_channel<T: Send>(bound: usize) -> (SyncSender<T>, Receiver<T>) {
+pub fn sync_channel<T>(bound: usize) -> (SyncSender<T>, Receiver<T>) {
     let a = Arc::new(UnsafeCell::new(sync::Packet::new(bound)));
     (SyncSender::new(a.clone()), Receiver::new(Flavor::Sync(a)))
 }
@@ -537,7 +537,7 @@ pub fn sync_channel<T: Send>(bound: usize) -> (SyncSender<T>, Receiver<T>) {
 // Sender
 ////////////////////////////////////////////////////////////////////////////////
 
-impl<T: Send> Sender<T> {
+impl<T> Sender<T> {
     fn new(inner: Flavor<T>) -> Sender<T> {
         Sender {
             inner: UnsafeCell::new(inner),
@@ -619,7 +619,7 @@ impl<T: Send> Sender<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Clone for Sender<T> {
+impl<T> Clone for Sender<T> {
     fn clone(&self) -> Sender<T> {
         let (packet, sleeper, guard) = match *unsafe { self.inner() } {
             Flavor::Oneshot(ref p) => {
@@ -665,7 +665,7 @@ impl<T: Send> Clone for Sender<T> {
 
 #[unsafe_destructor]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Drop for Sender<T> {
+impl<T> Drop for Sender<T> {
     fn drop(&mut self) {
         match *unsafe { self.inner_mut() } {
             Flavor::Oneshot(ref mut p) => unsafe { (*p.get()).drop_chan(); },
@@ -680,7 +680,7 @@ impl<T: Send> Drop for Sender<T> {
 // SyncSender
 ////////////////////////////////////////////////////////////////////////////////
 
-impl<T: Send> SyncSender<T> {
+impl<T> SyncSender<T> {
     fn new(inner: Arc<UnsafeCell<sync::Packet<T>>>) -> SyncSender<T> {
         SyncSender { inner: inner }
     }
@@ -720,7 +720,7 @@ impl<T: Send> SyncSender<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Clone for SyncSender<T> {
+impl<T> Clone for SyncSender<T> {
     fn clone(&self) -> SyncSender<T> {
         unsafe { (*self.inner.get()).clone_chan(); }
         return SyncSender::new(self.inner.clone());
@@ -729,7 +729,7 @@ impl<T: Send> Clone for SyncSender<T> {
 
 #[unsafe_destructor]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Drop for SyncSender<T> {
+impl<T> Drop for SyncSender<T> {
     fn drop(&mut self) {
         unsafe { (*self.inner.get()).drop_chan(); }
     }
@@ -739,7 +739,7 @@ impl<T: Send> Drop for SyncSender<T> {
 // Receiver
 ////////////////////////////////////////////////////////////////////////////////
 
-impl<T: Send> Receiver<T> {
+impl<T> Receiver<T> {
     fn new(inner: Flavor<T>) -> Receiver<T> {
         Receiver { inner: UnsafeCell::new(inner) }
     }
@@ -858,7 +858,7 @@ impl<T: Send> Receiver<T> {
     }
 }
 
-impl<T: Send> select::Packet for Receiver<T> {
+impl<T> select::Packet for Receiver<T> {
     fn can_recv(&self) -> bool {
         loop {
             let new_port = match *unsafe { self.inner() } {
@@ -945,7 +945,7 @@ impl<T: Send> select::Packet for Receiver<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: Send> Iterator for Iter<'a, T> {
+impl<'a, T> Iterator for Iter<'a, T> {
     type Item = T;
 
     fn next(&mut self) -> Option<T> { self.rx.recv().ok() }
@@ -953,7 +953,7 @@ impl<'a, T: Send> Iterator for Iter<'a, T> {
 
 #[unsafe_destructor]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Drop for Receiver<T> {
+impl<T> Drop for Receiver<T> {
     fn drop(&mut self) {
         match *unsafe { self.inner_mut() } {
             Flavor::Oneshot(ref mut p) => unsafe { (*p.get()).drop_port(); },
diff --git a/src/libstd/sync/mpsc/mpsc_queue.rs b/src/libstd/sync/mpsc/mpsc_queue.rs
index 1be8b0dd8628..7866a85dc8fa 100644
--- a/src/libstd/sync/mpsc/mpsc_queue.rs
+++ b/src/libstd/sync/mpsc/mpsc_queue.rs
@@ -89,7 +89,7 @@ impl<T> Node<T> {
     }
 }
 
-impl<T: Send> Queue<T> {
+impl<T> Queue<T> {
     /// Creates a new queue that is safe to share among multiple producers and
     /// one consumer.
     pub fn new() -> Queue<T> {
@@ -140,7 +140,7 @@ impl<T: Send> Queue<T> {
 
 #[unsafe_destructor]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Drop for Queue<T> {
+impl<T> Drop for Queue<T> {
     fn drop(&mut self) {
         unsafe {
             let mut cur = *self.tail.get();
diff --git a/src/libstd/sync/mpsc/oneshot.rs b/src/libstd/sync/mpsc/oneshot.rs
index 13578ce05179..21f690f0ee4d 100644
--- a/src/libstd/sync/mpsc/oneshot.rs
+++ b/src/libstd/sync/mpsc/oneshot.rs
@@ -88,7 +88,7 @@ enum MyUpgrade<T:Send> {
     GoUp(Receiver<T>),
 }
 
-impl<T: Send> Packet<T> {
+impl<T> Packet<T> {
     pub fn new() -> Packet<T> {
         Packet {
             data: None,
@@ -368,7 +368,7 @@ impl<T: Send> Packet<T> {
 }
 
 #[unsafe_destructor]
-impl<T: Send> Drop for Packet<T> {
+impl<T> Drop for Packet<T> {
     fn drop(&mut self) {
         assert_eq!(self.state.load(Ordering::SeqCst), DISCONNECTED);
     }
diff --git a/src/libstd/sync/mpsc/shared.rs b/src/libstd/sync/mpsc/shared.rs
index 80cbd0761638..be9730285777 100644
--- a/src/libstd/sync/mpsc/shared.rs
+++ b/src/libstd/sync/mpsc/shared.rs
@@ -64,7 +64,7 @@ pub enum Failure {
     Disconnected,
 }
 
-impl<T: Send> Packet<T> {
+impl<T> Packet<T> {
     // Creation of a packet *must* be followed by a call to postinit_lock
     // and later by inherit_blocker
     pub fn new() -> Packet<T> {
@@ -474,7 +474,7 @@ impl<T: Send> Packet<T> {
 }
 
 #[unsafe_destructor]
-impl<T: Send> Drop for Packet<T> {
+impl<T> Drop for Packet<T> {
     fn drop(&mut self) {
         // Note that this load is not only an assert for correctness about
         // disconnection, but also a proper fence before the read of
diff --git a/src/libstd/sync/mpsc/spsc_queue.rs b/src/libstd/sync/mpsc/spsc_queue.rs
index cd6d1ee05c78..278ac03cf03f 100644
--- a/src/libstd/sync/mpsc/spsc_queue.rs
+++ b/src/libstd/sync/mpsc/spsc_queue.rs
@@ -78,7 +78,7 @@ unsafe impl<T: Send> Send for Queue<T> { }
 
 unsafe impl<T: Send> Sync for Queue<T> { }
 
-impl<T: Send> Node<T> {
+impl<T> Node<T> {
     fn new() -> *mut Node<T> {
         unsafe {
             boxed::into_raw(box Node {
@@ -89,7 +89,7 @@ impl<T: Send> Node<T> {
     }
 }
 
-impl<T: Send> Queue<T> {
+impl<T> Queue<T> {
     /// Creates a new queue.
     ///
     /// This is unsafe as the type system doesn't enforce a single
@@ -227,7 +227,7 @@ impl<T: Send> Queue<T> {
 }
 
 #[unsafe_destructor]
-impl<T: Send> Drop for Queue<T> {
+impl<T> Drop for Queue<T> {
     fn drop(&mut self) {
         unsafe {
             let mut cur = *self.first.get();
diff --git a/src/libstd/sync/mpsc/stream.rs b/src/libstd/sync/mpsc/stream.rs
index a5a73314a6db..25b5f6f27ba8 100644
--- a/src/libstd/sync/mpsc/stream.rs
+++ b/src/libstd/sync/mpsc/stream.rs
@@ -74,7 +74,7 @@ enum Message<T:Send> {
     GoUp(Receiver<T>),
 }
 
-impl<T: Send> Packet<T> {
+impl<T> Packet<T> {
     pub fn new() -> Packet<T> {
         Packet {
             queue: unsafe { spsc::Queue::new(128) },
@@ -472,7 +472,7 @@ impl<T: Send> Packet<T> {
 }
 
 #[unsafe_destructor]
-impl<T: Send> Drop for Packet<T> {
+impl<T> Drop for Packet<T> {
     fn drop(&mut self) {
         // Note that this load is not only an assert for correctness about
         // disconnection, but also a proper fence before the read of
diff --git a/src/libstd/sync/mpsc/sync.rs b/src/libstd/sync/mpsc/sync.rs
index 71236269487e..8e49edc44b6a 100644
--- a/src/libstd/sync/mpsc/sync.rs
+++ b/src/libstd/sync/mpsc/sync.rs
@@ -113,10 +113,10 @@ pub enum Failure {
 
 /// Atomically blocks the current thread, placing it into `slot`, unlocking `lock`
 /// in the meantime. This re-locks the mutex upon returning.
-fn wait<'a, 'b, T: Send>(lock: &'a Mutex<State<T>>,
-                         mut guard: MutexGuard<'b, State<T>>,
-                         f: fn(SignalToken) -> Blocker)
-                         -> MutexGuard<'a, State<T>>
+fn wait<'a, 'b, T>(lock: &'a Mutex<State<T>>,
+                   mut guard: MutexGuard<'b, State<T>>,
+                   f: fn(SignalToken) -> Blocker)
+                   -> MutexGuard<'a, State<T>>
 {
     let (wait_token, signal_token) = blocking::tokens();
     match mem::replace(&mut guard.blocker, f(signal_token)) {
@@ -136,7 +136,7 @@ fn wakeup<T>(token: SignalToken, guard: MutexGuard<State<T>>) {
     token.signal();
 }
 
-impl<T: Send> Packet<T> {
+impl<T> Packet<T> {
     pub fn new(cap: usize) -> Packet<T> {
         Packet {
             channels: AtomicUsize::new(1),
@@ -412,7 +412,7 @@ impl<T: Send> Packet<T> {
 }
 
 #[unsafe_destructor]
-impl<T: Send> Drop for Packet<T> {
+impl<T> Drop for Packet<T> {
     fn drop(&mut self) {
         assert_eq!(self.channels.load(Ordering::SeqCst), 0);
         let mut guard = self.lock.lock().unwrap();
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index b24cfbb6899a..6a721aff89e0 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -122,6 +122,8 @@ pub struct Mutex<T: Send> {
     data: UnsafeCell<T>,
 }
 
+// these are the only places where `T: Send` matters; all other
+// functionality works fine on a single thread.
 unsafe impl<T: Send> Send for Mutex<T> { }
 
 unsafe impl<T: Send> Sync for Mutex<T> { }
@@ -181,7 +183,7 @@ pub const MUTEX_INIT: StaticMutex = StaticMutex {
     poison: poison::FLAG_INIT,
 };
 
-impl<T: Send> Mutex<T> {
+impl<T> Mutex<T> {
     /// Creates a new mutex in an unlocked state ready for use.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(t: T) -> Mutex<T> {
@@ -244,7 +246,7 @@ impl<T: Send> Mutex<T> {
 
 #[unsafe_destructor]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> Drop for Mutex<T> {
+impl<T> Drop for Mutex<T> {
     fn drop(&mut self) {
         // This is actually safe b/c we know that there is no further usage of
         // this mutex (it's up to the user to arrange for a mutex to get
@@ -254,7 +256,7 @@ impl<T: Send> Drop for Mutex<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: fmt::Debug + Send + 'static> fmt::Debug for Mutex<T> {
+impl<T: fmt::Debug + 'static> fmt::Debug for Mutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_lock() {
             Ok(guard) => write!(f, "Mutex {{ data: {:?} }}", *guard),
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index a79ffaa0860e..d70350bc7d65 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -130,7 +130,7 @@ pub struct RwLockWriteGuard<'a, T: 'a> {
 
 impl<'a, T> !marker::Send for RwLockWriteGuard<'a, T> {}
 
-impl<T: Send + Sync> RwLock<T> {
+impl<T> RwLock<T> {
     /// Creates a new instance of an `RwLock<T>` which is unlocked.
     ///
     /// # Examples
@@ -258,7 +258,7 @@ impl<T> Drop for RwLock<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: fmt::Debug + Send + Sync> fmt::Debug for RwLock<T> {
+impl<T: fmt::Debug> fmt::Debug for RwLock<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_read() {
             Ok(guard) => write!(f, "RwLock {{ data: {:?} }}", *guard),