diff --git a/src/mutex.cpp b/src/mutex.cpp
index b165b1b..e8637f9 100644
--- a/src/mutex.cpp
+++ b/src/mutex.cpp
@@ -12,7 +12,9 @@
 #include <limits>
 #include <mutex>
 
+#if !defined(_LIBCPP_ABI_MICROSOFT)
 #include "include/atomic_support.h"
+#endif
 
 #ifndef _LIBCPP_HAS_NO_THREADS
 #  if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
@@ -202,8 +204,13 @@ static constinit __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER;
 static constinit __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;
 #endif
 
+#ifdef _LIBCPP_ABI_MICROSOFT
+void __call_once(volatile std::atomic<once_flag::_State_type>& flag, void* arg,
+                 void (*func)(void*))
+#else
 void __call_once(volatile once_flag::_State_type& flag, void* arg,
                  void (*func)(void*))
+#endif
 {
 #if defined(_LIBCPP_HAS_NO_THREADS)
 
@@ -223,16 +230,28 @@ void __call_once(volatile once_flag::_State_type& flag, void* arg,
     if (flag == once_flag::_Unset) {
         auto guard = std::__make_exception_guard([&flag] {
             __libcpp_mutex_lock(&mut);
+#ifdef _LIBCPP_ABI_MICROSOFT
+            flag.store(once_flag::_Unset);
+#else
             __libcpp_relaxed_store(&flag, once_flag::_Unset);
+#endif
             __libcpp_mutex_unlock(&mut);
             __libcpp_condvar_broadcast(&cv);
         });
 
+#ifdef _LIBCPP_ABI_MICROSOFT
+        flag.store(once_flag::_Pending, memory_order_relaxed);
+#else
         __libcpp_relaxed_store(&flag, once_flag::_Pending);
+#endif
         __libcpp_mutex_unlock(&mut);
         func(arg);
         __libcpp_mutex_lock(&mut);
+#ifdef _LIBCPP_ABI_MICROSOFT
+        flag.store(once_flag::_Complete, memory_order_release);
+#else
         __libcpp_atomic_store(&flag, once_flag::_Complete, _AO_Release);
+#endif
         __libcpp_mutex_unlock(&mut);
         __libcpp_condvar_broadcast(&cv);
         guard.__complete();