diff --git a/src/mutex.rs b/src/mutex.rs
index 1a360a6..5f47406 100644
--- a/src/mutex.rs
+++ b/src/mutex.rs
@@ -268,6 +268,9 @@ pub struct Lock<'a, T: ?Sized> {
     acquire_slow: Option<AcquireSlow<&'a Mutex<T>, T>>,
 }
 
+unsafe impl<T: Send + ?Sized> Send for Lock<'_, T> {}
+unsafe impl<T: Sync + ?Sized> Sync for Lock<'_, T> {}
+
 impl<'a, T: ?Sized> Unpin for Lock<'a, T> {}
 
 impl<T: ?Sized> fmt::Debug for Lock<'_, T> {
@@ -319,6 +322,9 @@ enum LockArcInnards<T: ?Sized> {
     Empty,
 }
 
+unsafe impl<T: Send + ?Sized> Send for LockArc<T> {}
+unsafe impl<T: Sync + ?Sized> Sync for LockArc<T> {}
+
 impl<T: ?Sized> Unpin for LockArc<T> {}
 
 impl<T: ?Sized> fmt::Debug for LockArc<T> {
diff --git a/src/rwlock/futures.rs b/src/rwlock/futures.rs
index 73fbc17..a65d7dc 100644
--- a/src/rwlock/futures.rs
+++ b/src/rwlock/futures.rs
@@ -20,8 +20,8 @@ pub struct Read<'a, T: ?Sized> {
     pub(super) value: *const T,
 }
 
-unsafe impl<T: Send + Sync + ?Sized> Send for Read<'_, T> {}
-unsafe impl<T: Send + Sync + ?Sized> Sync for Read<'_, T> {}
+unsafe impl<T: Sync + ?Sized> Send for Read<'_, T> {}
+unsafe impl<T: Sync + ?Sized> Sync for Read<'_, T> {}
 
 impl<T: ?Sized> fmt::Debug for Read<'_, T> {
     #[inline]
@@ -90,7 +90,7 @@ pub struct UpgradableRead<'a, T: ?Sized> {
 }
 
 unsafe impl<T: Send + Sync + ?Sized> Send for UpgradableRead<'_, T> {}
-unsafe impl<T: Send + Sync + ?Sized> Sync for UpgradableRead<'_, T> {}
+unsafe impl<T: Sync + ?Sized> Sync for UpgradableRead<'_, T> {}
 
 impl<T: ?Sized> fmt::Debug for UpgradableRead<'_, T> {
     #[inline]
@@ -156,8 +156,8 @@ pub struct Write<'a, T: ?Sized> {
     pub(super) value: *mut T,
 }
 
-unsafe impl<T: Send + Sync + ?Sized> Send for Write<'_, T> {}
-unsafe impl<T: Send + Sync + ?Sized> Sync for Write<'_, T> {}
+unsafe impl<T: Send + ?Sized> Send for Write<'_, T> {}
+unsafe impl<T: Sync + ?Sized> Sync for Write<'_, T> {}
 
 impl<T: ?Sized> fmt::Debug for Write<'_, T> {
     #[inline]
@@ -224,6 +224,9 @@ pub struct Upgrade<'a, T: ?Sized> {
     pub(super) value: *mut T,
 }
 
+unsafe impl<T: Send + ?Sized> Send for Upgrade<'_, T> {}
+unsafe impl<T: Sync + ?Sized> Sync for Upgrade<'_, T> {}
+
 impl<T: ?Sized> fmt::Debug for Upgrade<'_, T> {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {