diff --git a/include/boost/preprocessor/detail/expand.hpp b/include/boost/preprocessor/detail/expand.hpp
index 055bc7e..7e46412 100644
--- a/include/boost/preprocessor/detail/expand.hpp
+++ b/include/boost/preprocessor/detail/expand.hpp
@@ -1,5 +1,5 @@
 #ifndef BOOST_PREPROCESSOR_DETAIL_EXPAND_HPP
-#define BOOST_PREPROCESSOR_DETAIL_EXPAND_HPP
+# define BOOST_PREPROCESSOR_DETAIL_EXPAND_HPP
 
 /* Copyright (C) 2002 Vesa Karvonen
  *