--- include/ruby/missing.h.orig	2019-09-19 14:06:28.928665240 +0200
+++ include/ruby/missing.h	2019-09-19 14:06:41.576665628 +0200
@@ -161,31 +161,6 @@
 # define HUGE_VAL ((double)INFINITY)
 #endif
 
-#ifndef isinf
-# ifndef HAVE_ISINF
-#  if defined(HAVE_FINITE) && defined(HAVE_ISNAN)
-#    ifdef HAVE_IEEEFP_H
-#    include <ieeefp.h>
-#    endif
-#  define isinf(x) (!finite(x) && !isnan(x))
-#  elif defined(__cplusplus) && __cplusplus >= 201103L
-#    include <cmath> // it must include constexpr bool isinf(double);
-#  else
-RUBY_EXTERN int isinf(double);
-#  endif
-# endif
-#endif
-
-#ifndef isnan
-# ifndef HAVE_ISNAN
-#  if defined(__cplusplus) && __cplusplus >= 201103L
-#    include <cmath> // it must include constexpr bool isnan(double);
-#  else
-RUBY_EXTERN int isnan(double);
-#  endif
-# endif
-#endif
-
 #ifndef isfinite
 # ifndef HAVE_ISFINITE
 #   define HAVE_ISFINITE 1