diff --git a/core/src/vmath.h b/core/src/vmath.h
index 9b2aed2..4c92d6b 100644
--- a/core/src/vmath.h
+++ b/core/src/vmath.h
@@ -4,6 +4,11 @@
 #include "stddef.h"
 #include <math.h>
 
+#if defined _WIN32 && ! defined isnanf
+# define isnanf(x) _isnanf(x)
+# define HAVE_ISNANF
+#endif
+
 #if VMATH_SDL == 1
 
 #include <SDL2/SDL_rect.h>