--- ray/src/common/rtmath.h	2016/03/06 01:13:17	3.9
+++ ray/src/common/rtmath.h	2016/03/10 18:09:43	3.10
@@ -1,4 +1,4 @@
-/* RCSid $Id: rtmath.h,v 3.9 2016/03/06 01:13:17 schorsch Exp $ */
+/* RCSid $Id: rtmath.h,v 3.10 2016/03/10 18:09:43 schorsch Exp $ */
 /*
  * Header for Radiance vector and math routines
  */
@@ -46,7 +46,9 @@ extern double	atan2a(double y, double x);
 #define  ttan(x)		(tsin(x)/tcos(x))
 #endif
 
-#if defined(_WIN32) || defined(_WIN64)
+/* VC 2015 has those defined (XXX possibly earlier?) */
+#if ((defined(_WIN32) || defined(_WIN64))
+		&& (!defined(_MS_VER) || _MS_VER < 1900))
 extern double	erf(double x);
 extern double	erfc(double x);
 #endif