Index: include/utility
===================================================================
--- include/utility	(revision 153896)
+++ include/utility	(working copy)
@@ -206,8 +206,11 @@
 }
 
 struct _LIBCPP_VISIBLE piecewise_construct_t { };
-//constexpr
+#ifdef _LIBCPP_HAS_NO_CONSTEXPR
 extern const piecewise_construct_t piecewise_construct;// = piecewise_construct_t();
+#else
+constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
+#endif
 
 template <class _T1, class _T2>
 struct _LIBCPP_VISIBLE pair
@@ -221,7 +224,7 @@
     // pair(const pair&) = default;
     // pair(pair&&) = default;
 
-    _LIBCPP_INLINE_VISIBILITY pair() : first(), second() {}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR pair() : first(), second() {}
 
     _LIBCPP_INLINE_VISIBILITY pair(const _T1& __x, const _T2& __y)
         : first(__x), second(__y) {}
Index: src/utility.cpp
===================================================================
--- src/utility.cpp	(revision 153896)
+++ src/utility.cpp	(working copy)
@@ -11,6 +11,8 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+#ifdef _LIBCPP_HAS_NO_CONSTEXPR
 const piecewise_construct_t piecewise_construct = {};
+#endif
 
 _LIBCPP_END_NAMESPACE_STD