Index: libcxx/include/mutex
===================================================================
--- libcxx/include/mutex
+++ libcxx/include/mutex
@@ -188,6 +188,7 @@
 
 #include <__config>
 #include <__mutex_base>
+#include <cstdint>
 #include <functional>
 #include <memory>
 #ifndef _LIBCPP_CXX03_LANG
@@ -575,11 +576,18 @@
     _LIBCPP_CONSTEXPR
         once_flag() _NOEXCEPT : __state_(0) {}
 
+#if defined(_LIBCPP_ABI_MICROSOFT) || defined(_LIBCPP_ABI_UNSTABLE)
+   typedef uintptr_t _State_type;
+#else
+   typedef unsigned long _State_type;
+#endif
+
+
 private:
     once_flag(const once_flag&); // = delete;
     once_flag& operator=(const once_flag&); // = delete;
 
-    unsigned long __state_;
+    _State_type __state_;
 
 #ifndef _LIBCPP_CXX03_LANG
     template<class _Callable, class... _Args>
@@ -649,7 +657,8 @@
     (*__p)();
 }
 
-_LIBCPP_FUNC_VIS void __call_once(volatile unsigned long&, void*, void(*)(void*));
+_LIBCPP_FUNC_VIS void __call_once(volatile once_flag::_State_type&, void*,
+                                  void (*)(void*));
 
 #ifndef _LIBCPP_CXX03_LANG
 
@@ -658,7 +667,7 @@
 void
 call_once(once_flag& __flag, _Callable&& __func, _Args&&... __args)
 {
-    if (__libcpp_acquire_load(&__flag.__state_) != ~0ul)
+    if (__libcpp_acquire_load(&__flag.__state_) != ~once_flag::_State_type(0))
     {
         typedef tuple<_Callable&&, _Args&&...> _Gp;
         _Gp __f(_VSTD::forward<_Callable>(__func), _VSTD::forward<_Args>(__args)...);
@@ -674,7 +683,7 @@
 void
 call_once(once_flag& __flag, _Callable& __func)
 {
-    if (__libcpp_acquire_load(&__flag.__state_) != ~0ul)
+    if (__libcpp_acquire_load(&__flag.__state_) != ~once_flag::_State_type(0))
     {
         __call_once_param<_Callable> __p(__func);
         __call_once(__flag.__state_, &__p, &__call_once_proxy<_Callable>);
@@ -686,7 +695,7 @@
 void
 call_once(once_flag& __flag, const _Callable& __func)
 {
-    if (__libcpp_acquire_load(&__flag.__state_) != ~0ul)
+    if (__libcpp_acquire_load(&__flag.__state_) != ~once_flag::_State_type(0))
     {
         __call_once_param<const _Callable> __p(__func);
         __call_once(__flag.__state_, &__p, &__call_once_proxy<const _Callable>);
Index: libcxx/src/mutex.cpp
===================================================================
--- libcxx/src/mutex.cpp
+++ libcxx/src/mutex.cpp
@@ -197,8 +197,8 @@
 _LIBCPP_SAFE_STATIC static __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;
 #endif
 
-void
-__call_once(volatile unsigned long& flag, void* arg, void(*func)(void*))
+void __call_once(volatile once_flag::_State_type& flag, void* arg,
+                 void (*func)(void*))
 {
 #if defined(_LIBCPP_HAS_NO_THREADS)
     if (flag == 0)
@@ -209,12 +209,12 @@
 #endif  // _LIBCPP_NO_EXCEPTIONS
             flag = 1;
             func(arg);
-            flag = ~0ul;
+            flag = ~once_flag::_State_type(0);
 #ifndef _LIBCPP_NO_EXCEPTIONS
         }
         catch (...)
         {
-            flag = 0ul;
+            flag = 0;
             throw;
         }
 #endif  // _LIBCPP_NO_EXCEPTIONS
@@ -229,11 +229,12 @@
         try
         {
 #endif  // _LIBCPP_NO_EXCEPTIONS
-            __libcpp_relaxed_store(&flag, 1ul);
+            __libcpp_relaxed_store(&flag, once_flag::_State_type(1));
             __libcpp_mutex_unlock(&mut);
             func(arg);
             __libcpp_mutex_lock(&mut);
-            __libcpp_atomic_store(&flag, ~0ul, _AO_Release);
+            __libcpp_atomic_store(&flag, ~once_flag::_State_type(0),
+                                  _AO_Release);
             __libcpp_mutex_unlock(&mut);
             __libcpp_condvar_broadcast(&cv);
 #ifndef _LIBCPP_NO_EXCEPTIONS
@@ -241,7 +242,7 @@
         catch (...)
         {
             __libcpp_mutex_lock(&mut);
-            __libcpp_relaxed_store(&flag, 0ul);
+            __libcpp_relaxed_store(&flag, once_flag::_State_type(0));
             __libcpp_mutex_unlock(&mut);
             __libcpp_condvar_broadcast(&cv);
             throw;
@@ -251,7 +252,6 @@
     else
         __libcpp_mutex_unlock(&mut);
 #endif // !_LIBCPP_HAS_NO_THREADS
-
 }
 
 _LIBCPP_END_NAMESPACE_STD