diff --git a/src/sync/mod.rs b/src/sync/mod.rs
index 77bda2d964640c9b5fec2100e9d61cb123b97dae..dc4ecd4fdbd77d99123747c191d15b8f7551f7e7 100644
--- a/src/sync/mod.rs
+++ b/src/sync/mod.rs
@@ -1,3 +1,6 @@
+// TODO: set this for entire crate when possible
+#![deny(unsafe_op_in_unsafe_fn)]
+
 pub mod barrier;
 pub mod cond;
 // TODO: Merge with pthread_mutex
@@ -95,14 +98,14 @@ impl FutexAtomicTy for AtomicI32 {
 
 pub unsafe fn futex_wake_ptr(ptr: *mut impl FutexTy, n: i32) -> usize {
     // TODO: unwrap_unchecked?
-    Sys::futex_wake(ptr.cast(), n as u32).unwrap() as usize
+    unsafe { Sys::futex_wake(ptr.cast(), n as u32) }.unwrap() as usize
 }
 pub unsafe fn futex_wait_ptr<T: FutexTy>(
     ptr: *mut T,
     value: T,
     deadline_opt: Option<&timespec>,
 ) -> FutexWaitResult {
-    match Sys::futex_wait(ptr.cast(), value.conv(), deadline_opt) {
+    match unsafe { Sys::futex_wait(ptr.cast(), value.conv(), deadline_opt) } {
         Ok(()) => FutexWaitResult::Waited,
         Err(Errno(EAGAIN)) => FutexWaitResult::Stale,
         Err(Errno(ETIMEDOUT)) if deadline_opt.is_some() => FutexWaitResult::TimedOut,
diff --git a/src/sync/mutex.rs b/src/sync/mutex.rs
index 6c0c6b4dc16350c1fca2383c52f887f1b297143e..9a5d0e4f48f0444708b4dcb558356224564d93ef 100644
--- a/src/sync/mutex.rs
+++ b/src/sync/mutex.rs
@@ -76,8 +76,8 @@ impl<T> Mutex<T> {
     /// on failure. You should probably not worry about this, it's used for
     /// internal optimizations.
     pub unsafe fn manual_try_lock(&self) -> Result<&mut T, c_int> {
-        if manual_try_lock_generic(&self.lock) {
-            Ok(&mut *self.content.get())
+        if unsafe { manual_try_lock_generic(&self.lock) } {
+            Ok(unsafe { &mut *self.content.get() })
         } else {
             Err(0)
         }
@@ -86,12 +86,12 @@ impl<T> Mutex<T> {
     /// your responsibility to unlock it after usage. Mostly useful for FFI:
     /// Prefer normal .lock() where possible.
     pub unsafe fn manual_lock(&self) -> &mut T {
-        manual_lock_generic(&self.lock);
-        &mut *self.content.get()
+        unsafe { manual_lock_generic(&self.lock) };
+        unsafe { &mut *self.content.get() }
     }
     /// Unlock the mutex, if it's locked.
     pub unsafe fn manual_unlock(&self) {
-        manual_unlock_generic(&self.lock)
+        unsafe { manual_unlock_generic(&self.lock) }
     }
     pub fn as_ptr(&self) -> *mut T {
         self.content.get()
diff --git a/src/sync/waitval.rs b/src/sync/waitval.rs
index f8b2128d7a10be2650d5936fa0b440191271826b..fbc9db633e46d6884c2ff45f193a3149440921b4 100644
--- a/src/sync/waitval.rs
+++ b/src/sync/waitval.rs
@@ -28,7 +28,7 @@ impl<T> Waitval<T> {
     // SAFETY: Caller must ensure both (1) that the value has not yet been initialized, and (2)
     // that this is never run by more than one thread simultaneously.
     pub unsafe fn post(&self, value: T) {
-        self.value.get().write(MaybeUninit::new(value));
+        unsafe { self.value.get().write(MaybeUninit::new(value)) };
         self.state.store(1, Ordering::Release);
         crate::sync::futex_wake(&self.state, i32::MAX);
     }