Index: include/cmath
===================================================================
--- include/cmath
+++ include/cmath
@@ -1109,8 +1109,16 @@
 using ::copysign;
 using ::copysignf;
 
-inline _LIBCPP_INLINE_VISIBILITY float       copysign(float __lcpp_x, float __lcpp_y) _NOEXCEPT             {return copysignf(__lcpp_x, __lcpp_y);}
-inline _LIBCPP_INLINE_VISIBILITY long double copysign(long double __lcpp_x, long double __lcpp_y) _NOEXCEPT {return copysignl(__lcpp_x, __lcpp_y);}
+#if !defined(_VC_CRT_MAJOR_VERSION) || (_VC_CRT_MAJOR_VERSION < 12)
+inline _LIBCPP_INLINE_VISIBILITY float copysign(float __lcpp_x,
+                                                float __lcpp_y) _NOEXCEPT {
+  return copysignf(__lcpp_x, __lcpp_y);
+}
+inline _LIBCPP_INLINE_VISIBILITY long double
+copysign(long double __lcpp_x, long double __lcpp_y) _NOEXCEPT {
+  return copysignl(__lcpp_x, __lcpp_y);
+}
+#endif
 
 template <class _A1, class _A2>
 inline _LIBCPP_INLINE_VISIBILITY
Index: include/support/win32/math_win32.h
===================================================================
--- include/support/win32/math_win32.h
+++ include/support/win32/math_win32.h
@@ -17,7 +17,9 @@
 
 #include <math.h>
 #include <float.h> // _FPCLASS_PN etc.
+#include <crtversion.h>
 
+#if ((_VC_CRT_MAJOR_VERSION-0) < 12)
 // Necessary?
 typedef float float_t;
 typedef double double_t;
@@ -109,7 +111,7 @@
 {
     return _fpclass(num);
 }
-
+#endif
 #endif // _LIBCPP_MSVCRT
 
 #endif // _LIBCPP_SUPPORT_WIN32_MATH_WIN32_H