diff --git a/include/boost/charconv/detail/emulated128.hpp b/include/boost/charconv/detail/emulated128.hpp
index 9cd88ff..1b3dccc 100644
--- a/include/boost/charconv/detail/emulated128.hpp
+++ b/include/boost/charconv/detail/emulated128.hpp
@@ -5,14 +5,14 @@
 
 // If the architecture (e.g. ARM) does not have __int128 we need to emulate it
 
+#ifndef BOOST_CHARCONV_DETAIL_EMULATED128_HPP
+#define BOOST_CHARCONV_DETAIL_EMULATED128_HPP
+
 #include <boost/charconv/detail/config.hpp>
 #include <boost/charconv/config.hpp>
 #include <cstdint>
 #include <cassert>
 
-#ifndef BOOST_CHARCONV_DETAIL_EMULATED128_HPP
-#define BOOST_CHARCONV_DETAIL_EMULATED128_HPP
-
 namespace boost { namespace charconv { namespace detail {
 
 // Emulates a __int128 using 2x 64bit ints (high and low)