diff --git a/libc/include/semaphore.h b/libc/include/semaphore.h
index 5d66f7ec0..6ad9ea3ad 100644
--- a/libc/include/semaphore.h
+++ b/libc/include/semaphore.h
@@ -45,12 +45,12 @@ typedef struct {
 
 #define SEM_FAILED __BIONIC_CAST(reinterpret_cast, sem_t*, 0)
 
-int sem_clockwait(sem_t* __sem, clockid_t __clock, const struct timespec* __ts) __INTRODUCED_IN(30);
-int sem_destroy(sem_t* __sem);
-int sem_getvalue(sem_t* __sem, int* __value);
-int sem_init(sem_t* __sem, int __shared, unsigned int __value);
-int sem_post(sem_t* __sem);
-int sem_timedwait(sem_t* __sem, const struct timespec* __ts);
+int sem_clockwait(sem_t* _Nonnull __sem, clockid_t __clock, const struct timespec* _Nonnull __ts) __INTRODUCED_IN(30);
+int sem_destroy(sem_t* _Nonnull __sem);
+int sem_getvalue(sem_t* _Nonnull __sem, int* _Nonnull __value);
+int sem_init(sem_t* _Nonnull __sem, int __shared, unsigned int __value);
+int sem_post(sem_t* _Nonnull __sem);
+int sem_timedwait(sem_t* _Nonnull __sem, const struct timespec* _Nonnull __ts);
 /*
  * POSIX historically only supported using sem_timedwait() with CLOCK_REALTIME, however that is
  * typically inappropriate, since that clock can change dramatically, causing the timeout to either
@@ -59,14 +59,14 @@ int sem_timedwait(sem_t* __sem, const struct timespec* __ts);
  * Note that sem_clockwait() allows specifying an arbitrary clock and has superseded this
  * function.
  */
-int sem_timedwait_monotonic_np(sem_t* __sem, const struct timespec* __ts) __INTRODUCED_IN(28);
-int sem_trywait(sem_t* __sem);
-int sem_wait(sem_t* __sem);
+int sem_timedwait_monotonic_np(sem_t* _Nonnull __sem, const struct timespec* _Nonnull __ts) __INTRODUCED_IN(28);
+int sem_trywait(sem_t* _Nonnull __sem);
+int sem_wait(sem_t* _Nonnull __sem);
 
 /* These aren't actually implemented. */
-sem_t* sem_open(const char* __name, int _flags, ...);
-int sem_close(sem_t* __sem);
-int sem_unlink(const char* __name);
+sem_t* _Nullable sem_open(const char* _Nonnull __name, int _flags, ...);
+int sem_close(sem_t* _Nonnull __sem);
+int sem_unlink(const char* _Nonnull __name);
 
 __END_DECLS
 
diff --git a/tests/semaphore_test.cpp b/tests/semaphore_test.cpp
index f3f60208d..6f8797f08 100644
--- a/tests/semaphore_test.cpp
+++ b/tests/semaphore_test.cpp
@@ -165,8 +165,10 @@ TEST(semaphore, sem_clockwait) {
 TEST_F(semaphore_DeathTest, sem_timedwait_null_timeout) {
   sem_t s;
   ASSERT_EQ(0, sem_init(&s, 0, 0));
-
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnonnull"
   ASSERT_EXIT(sem_timedwait(&s, nullptr), testing::KilledBySignal(SIGSEGV), "");
+#pragma clang diagnostic pop
 }
 
 TEST(semaphore, sem_getvalue) {