--- a/configure.ac
+++ b/configure.ac
@@ -76,12 +76,6 @@ AC_FUNC_VPRINTF
 AC_FUNC_MEMCMP
 AC_CHECK_FUNCS([realloc])
 AC_CHECK_FUNCS(strcasecmp strdup strerror snprintf vsnprintf vasprintf open vsyslog strncasecmp setlocale)
-AC_CHECK_DECLS([INFINITY], [], [], [[#include <math.h>]])
-AC_CHECK_DECLS([nan], [], [], [[#include <math.h>]])
-AC_CHECK_DECLS([isnan], [], [], [[#include <math.h>]])
-AC_CHECK_DECLS([isinf], [], [], [[#include <math.h>]])
-AC_CHECK_DECLS([_isnan], [], [], [[#include <float.h>]])
-AC_CHECK_DECLS([_finite], [], [], [[#include <float.h>]])
 AC_MSG_CHECKING(for GCC atomic builtins)
 AC_LINK_IFELSE(
 [
--- a/math_compat.h
+++ b/math_compat.h
@@ -6,31 +6,9 @@
  * @brief Do not use, json-c internal, may be changed or removed at any time.
  */
 
-/* Define isnan, isinf, infinity and nan on Windows/MSVC */
-
-#ifndef HAVE_DECL_ISNAN
-# ifdef HAVE_DECL__ISNAN
-#include <float.h>
-#define isnan(x) _isnan(x)
-# endif
-#endif
-
-#ifndef HAVE_DECL_ISINF
-# ifdef HAVE_DECL__FINITE
-#include <float.h>
-#define isinf(x) (!_finite(x))
-# endif
-#endif
-
-#ifndef HAVE_DECL_INFINITY
-#include <float.h>
-#define INFINITY (DBL_MAX + DBL_MAX)
-#define HAVE_DECL_INFINITY
-#endif
-
-#ifndef HAVE_DECL_NAN
-#define NAN (INFINITY - INFINITY)
-#define HAVE_DECL_NAN
-#endif
+#undef isnan
+#define isnan(x) __builtin_isnan(x)
+#undef isinf
+#define isinf(x) __builtin_isinf(x)
 
 #endif