diff --git a/FL/math.h b/FL/math.h
index b574000..216a2ad 100644
--- a/FL/math.h
+++ b/FL/math.h
@@ -47,7 +47,7 @@
 #    define M_SQRT1_2       0.70710678118654752440
 #  endif // !M_SQRT2
 
-#  if (defined(WIN32) || defined(CRAY)) && !defined(__MINGW32__) && !defined(__MWERKS__)
+#  if defined(FLTK_ENABLE_MATH_H_POLYFILL)
 
 inline double rint(double v) {return floor(v+.5);}
 inline double copysign(double a, double b) {return b<0 ? -a : a;}