diff --git a/libcxx/include/math.h b/libcxx/include/math.h
--- a/libcxx/include/math.h
+++ b/libcxx/include/math.h
@@ -1120,16 +1120,32 @@
 
 // copysign
 
-inline _LIBCPP_INLINE_VISIBILITY float copysign(float __lcpp_x,
-                                                float __lcpp_y) _NOEXCEPT {
+#if __has_builtin(__builtin_copysignf)
+_LIBCPP_CONSTEXPR
+#endif
+inline _LIBCPP_INLINE_VISIBILITY float __libcpp_copysign(float __lcpp_x, float __lcpp_y) _NOEXCEPT {
 #if __has_builtin(__builtin_copysignf)
   return __builtin_copysignf(__lcpp_x, __lcpp_y);
 #else
   return ::copysignf(__lcpp_x, __lcpp_y);
 #endif
 }
-inline _LIBCPP_INLINE_VISIBILITY long double
-copysign(long double __lcpp_x, long double __lcpp_y) _NOEXCEPT {
+
+#if __has_builtin(__builtin_copysign)
+_LIBCPP_CONSTEXPR
+#endif
+inline _LIBCPP_INLINE_VISIBILITY double __libcpp_copysign(double __lcpp_x, double __lcpp_y) _NOEXCEPT {
+#if __has_builtin(__builtin_copysign)
+  return __builtin_copysign(__lcpp_x, __lcpp_y);
+#else
+  return ::copysign(__lcpp_x, __lcpp_y);
+#endif
+}
+
+#if __has_builtin(__builtin_copysignl)
+_LIBCPP_CONSTEXPR
+#endif
+inline _LIBCPP_INLINE_VISIBILITY long double __libcpp_copysign(long double __lcpp_x, long double __lcpp_y) _NOEXCEPT {
 #if __has_builtin(__builtin_copysignl)
   return __builtin_copysignl(__lcpp_x, __lcpp_y);
 #else
@@ -1138,6 +1154,9 @@
 }
 
 template <class _A1, class _A2>
+#if __has_builtin(__builtin_copysign)
+_LIBCPP_CONSTEXPR
+#endif
 inline _LIBCPP_INLINE_VISIBILITY
 typename std::_EnableIf
 <
@@ -1145,8 +1164,7 @@
     std::is_arithmetic<_A2>::value,
     std::__promote<_A1, _A2>
 >::type
-copysign(_A1 __lcpp_x, _A2 __lcpp_y) _NOEXCEPT
-{
+__libcpp_copysign(_A1 __lcpp_x, _A2 __lcpp_y) _NOEXCEPT {
     typedef typename std::__promote<_A1, _A2>::type __result_type;
     static_assert((!(std::_IsSame<_A1, __result_type>::value &&
                      std::_IsSame<_A2, __result_type>::value)), "");
@@ -1157,6 +1175,26 @@
 #endif
 }
 
+inline _LIBCPP_INLINE_VISIBILITY float copysign(float __lcpp_x, float __lcpp_y) _NOEXCEPT {
+  return ::__libcpp_copysign(__lcpp_x, __lcpp_y);
+}
+
+inline _LIBCPP_INLINE_VISIBILITY long double copysign(long double __lcpp_x, long double __lcpp_y) _NOEXCEPT {
+  return ::__libcpp_copysign(__lcpp_x, __lcpp_y);
+}
+
+template <class _A1, class _A2>
+inline _LIBCPP_INLINE_VISIBILITY
+typename std::_EnableIf
+<
+    std::is_arithmetic<_A1>::value &&
+    std::is_arithmetic<_A2>::value,
+    std::__promote<_A1, _A2>
+>::type
+    copysign(_A1 __lcpp_x, _A2 __lcpp_y) _NOEXCEPT {
+  return ::__libcpp_copysign(__lcpp_x, __lcpp_y);
+}
+
 // erf
 
 inline _LIBCPP_INLINE_VISIBILITY float       erf(float __lcpp_x) _NOEXCEPT       {return ::erff(__lcpp_x);}