diff --git a/lock_api/src/lib.rs b/lock_api/src/lib.rs
index de724422..d9097a39 100644
--- a/lock_api/src/lib.rs
+++ b/lock_api/src/lib.rs
@@ -99,6 +99,8 @@ pub struct GuardSend(());
 /// Marker type which indicates that the Guard type for a lock is not `Send`.
 pub struct GuardNoSend(*mut ());
 
+unsafe impl Sync for GuardNoSend {}
+
 mod mutex;
 pub use crate::mutex::*;
 
diff --git a/lock_api/src/mutex.rs b/lock_api/src/mutex.rs
index e435d8ae..aded96d1 100644
--- a/lock_api/src/mutex.rs
+++ b/lock_api/src/mutex.rs
@@ -601,7 +601,7 @@ unsafe impl<'a, R: RawMutex + Sync + 'a, T: ?Sized + Sync + 'a> Sync
     for MappedMutexGuard<'a, R, T>
 {
 }
-unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Send for MappedMutexGuard<'a, R, T> where
+unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + Send + 'a> Send for MappedMutexGuard<'a, R, T> where
     R::GuardMarker: Send
 {
 }
diff --git a/lock_api/src/rwlock.rs b/lock_api/src/rwlock.rs
index a25c2f45..e97de980 100644
--- a/lock_api/src/rwlock.rs
+++ b/lock_api/src/rwlock.rs
@@ -875,8 +875,6 @@ pub struct RwLockReadGuard<'a, R: RawRwLock, T: ?Sized> {
     marker: PhantomData<(&'a T, R::GuardMarker)>,
 }
 
-unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for RwLockReadGuard<'a, R, T> {}
-
 impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> RwLockReadGuard<'a, R, T> {
     /// Returns a reference to the original reader-writer lock object.
     pub fn rwlock(s: &Self) -> &'a RwLock<R, T> {
@@ -1051,8 +1049,6 @@ pub struct RwLockWriteGuard<'a, R: RawRwLock, T: ?Sized> {
     marker: PhantomData<(&'a mut T, R::GuardMarker)>,
 }
 
-unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for RwLockWriteGuard<'a, R, T> {}
-
 impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> RwLockWriteGuard<'a, R, T> {
     /// Returns a reference to the original reader-writer lock object.
     pub fn rwlock(s: &Self) -> &'a RwLock<R, T> {
@@ -1514,7 +1510,7 @@ pub struct MappedRwLockReadGuard<'a, R: RawRwLock, T: ?Sized> {
 }
 
 unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for MappedRwLockReadGuard<'a, R, T> {}
-unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Send for MappedRwLockReadGuard<'a, R, T> where
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Send for MappedRwLockReadGuard<'a, R, T> where
     R::GuardMarker: Send
 {
 }
@@ -1652,7 +1648,7 @@ unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync
     for MappedRwLockWriteGuard<'a, R, T>
 {
 }
-unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Send for MappedRwLockWriteGuard<'a, R, T> where
+unsafe impl<'a, R: RawRwLock + 'a, T: ?Sized + Send + 'a> Send for MappedRwLockWriteGuard<'a, R, T> where
     R::GuardMarker: Send
 {
 }