diff --git a/include/ruby/missing.h b/include/ruby/missing.h
index e81ad2769d..d12f496c18 100644
--- a/include/ruby/missing.h
+++ b/include/ruby/missing.h
@@ -136,7 +136,7 @@ RUBY_EXTERN double lgamma_r(double, int *);
 RUBY_EXTERN double cbrt(double);
 #endif
 
-#if !defined(INFINITY) || !defined(NAN)
+#if !defined(HAVE_INFINITY) || !defined(HAVE_NAN)
 union bytesequence4_or_float {
   unsigned char bytesequence[4];
   float float_value;