diff --git a/include/boost/math/tools/config.hpp b/include/boost/math/tools/config.hpp
index 5edf98d75..964a2bf0b 100644
--- a/include/boost/math/tools/config.hpp
+++ b/include/boost/math/tools/config.hpp
@@ -200,7 +200,7 @@
 
 // C++23
 #if __cplusplus > 202002L || (defined(_MSVC_LANG) &&_MSVC_LANG > 202002L)
-#  if __GNUC__ >= 13
+#  if defined(__GNUC__) && __GNUC__ >= 13
      // libstdc++3 only defines to/from_chars for std::float128_t when one of these defines are set
      // otherwise we're right out of luck...
 #    if defined(_GLIBCXX_LDOUBLE_IS_IEEE_BINARY128) || defined(_GLIBCXX_HAVE_FLOAT128_MATH)