Index: include/__mutex_base
===================================================================
--- include/__mutex_base
+++ include/__mutex_base
@@ -34,15 +34,14 @@
 
 class _LIBCPP_TYPE_VIS _LIBCPP_THREAD_SAFETY_ANNOTATION(capability("mutex")) mutex
 {
-    __libcpp_mutex_t __m_;
+    __libcpp_mutex_t __m_ = _LIBCPP_MUTEX_INITIALIZER;
 
 public:
     _LIBCPP_INLINE_VISIBILITY
 #ifndef _LIBCPP_HAS_NO_CONSTEXPR
-    constexpr mutex() _NOEXCEPT : __m_(_LIBCPP_MUTEX_INITIALIZER) {}
-#else
-    mutex() _NOEXCEPT {__m_ = (__libcpp_mutex_t)_LIBCPP_MUTEX_INITIALIZER;}
+    constexpr
 #endif
+    mutex() _NOEXCEPT = default;
      ~mutex();
 
 private:
@@ -287,15 +286,15 @@
 
 class _LIBCPP_TYPE_VIS condition_variable
 {
-    __libcpp_condvar_t  __cv_;
+    __libcpp_condvar_t  __cv_ = _LIBCPP_CONDVAR_INITIALIZER;
+
 public:
     _LIBCPP_INLINE_VISIBILITY
 #ifndef _LIBCPP_HAS_NO_CONSTEXPR
-    constexpr condition_variable() : __cv_(_LIBCPP_CONDVAR_INITIALIZER) {}
-#else
-    condition_variable() {__cv_ = (__libcpp_condvar_t)_LIBCPP_CONDVAR_INITIALIZER;}
+    constexpr
 #endif
-    ~condition_variable();
+    condition_variable() _NOEXCEPT;
+    ~condition_variable() _NOEXCEPT;
 
 private:
     condition_variable(const condition_variable&); // = delete;