diff --git a/libcxx/include/__atomic/atomic_sync.h b/libcxx/include/__atomic/atomic_sync.h
index 1de5037329f8..aaf81f58731a 100644
--- a/libcxx/include/__atomic/atomic_sync.h
+++ b/libcxx/include/__atomic/atomic_sync.h
@@ -71,19 +71,21 @@ struct __atomic_wait_poll_impl {
 
 #ifndef _LIBCPP_HAS_NO_THREADS
 
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*);
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*);
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t __libcpp_atomic_monitor(void const volatile*);
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __libcpp_atomic_wait(void const volatile*, __cxx_contention_t);
+_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*) _NOEXCEPT;
+_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*) _NOEXCEPT;
+_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
+__libcpp_atomic_monitor(void const volatile*) _NOEXCEPT;
+_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_wait(void const volatile*, __cxx_contention_t) _NOEXCEPT;
 
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
-__cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile*);
+__cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
-__cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile*);
+__cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
-__libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*);
+__libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
-__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t);
+__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t) _NOEXCEPT;
 
 template <class _AtomicWaitable, class _Poll>
 struct __atomic_wait_backoff_impl {
diff --git a/libcxx/include/barrier b/libcxx/include/barrier
index bce67bb5d342..3843a9765d93 100644
--- a/libcxx/include/barrier
+++ b/libcxx/include/barrier
@@ -102,10 +102,10 @@ _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __barrier_algorithm_base*
 __construct_barrier_algorithm_base(ptrdiff_t& __expected);
 
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI bool
-__arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase);
+__arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) noexcept;
 
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
-__destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier);
+__destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) noexcept;
 
 template <class _CompletionF>
 class __barrier_base {
diff --git a/libcxx/src/atomic.cpp b/libcxx/src/atomic.cpp
index 7142f38c9609..ae062155661e 100644
--- a/libcxx/src/atomic.cpp
+++ b/libcxx/src/atomic.cpp
@@ -169,17 +169,18 @@ static void __libcpp_atomic_notify(void const volatile* __location) {
       &__entry->__platform_state,
       false /* when laundering, we can't handle notify_one */);
 }
-_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile* __location) {
+_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile* __location) noexcept {
   __libcpp_atomic_notify(__location);
 }
-_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile* __location) {
+_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile* __location) noexcept {
   __libcpp_atomic_notify(__location);
 }
-_LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t __libcpp_atomic_monitor(void const volatile* __location) {
+_LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t __libcpp_atomic_monitor(void const volatile* __location) noexcept {
   auto const __entry = __libcpp_contention_state(__location);
   return __libcpp_contention_monitor_for_wait(&__entry->__contention_state, &__entry->__platform_state);
 }
-_LIBCPP_EXPORTED_FROM_ABI void __libcpp_atomic_wait(void const volatile* __location, __cxx_contention_t __old_value) {
+_LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_wait(void const volatile* __location, __cxx_contention_t __old_value) noexcept {
   auto const __entry = __libcpp_contention_state(__location);
   __libcpp_contention_wait(&__entry->__contention_state, &__entry->__platform_state, __old_value);
 }
@@ -187,19 +188,19 @@ _LIBCPP_EXPORTED_FROM_ABI void __libcpp_atomic_wait(void const volatile* __locat
 /* When the incoming atomic happens to be the platform wait size, we still need to use the
    table for the contention detection, but we can use the atomic directly for the wait. */
 
-_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile* __location) {
+_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile* __location) noexcept {
   __libcpp_contention_notify(&__libcpp_contention_state(__location)->__contention_state, __location, true);
 }
-_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile* __location) {
+_LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile* __location) noexcept {
   __libcpp_contention_notify(&__libcpp_contention_state(__location)->__contention_state, __location, false);
 }
 // This function is never used, but still exported for ABI compatibility.
 _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
-__libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile* __location) {
+__libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile* __location) noexcept {
   return __libcpp_contention_monitor_for_wait(&__libcpp_contention_state(__location)->__contention_state, __location);
 }
 _LIBCPP_EXPORTED_FROM_ABI void
-__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile* __location, __cxx_contention_t __old_value) {
+__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile* __location, __cxx_contention_t __old_value) noexcept {
   __libcpp_contention_wait(&__libcpp_contention_state(__location)->__contention_state, __location, __old_value);
 }
 
diff --git a/libcxx/src/barrier.cpp b/libcxx/src/barrier.cpp
index baa26101cd57..bbcfb6001bba 100644
--- a/libcxx/src/barrier.cpp
+++ b/libcxx/src/barrier.cpp
@@ -63,10 +63,10 @@ _LIBCPP_EXPORTED_FROM_ABI __barrier_algorithm_base* __construct_barrier_algorith
   return new __barrier_algorithm_base(__expected);
 }
 _LIBCPP_EXPORTED_FROM_ABI bool
-__arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) {
+__arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) noexcept {
   return __barrier->__arrive(__old_phase);
 }
-_LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) {
+_LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) noexcept {
   delete __barrier;
 }