diff --git a/include/boost/type_traits/is_integral.hpp b/include/boost/type_traits/is_integral.hpp
index b6ca6c7..51710c2 100644
--- a/include/boost/type_traits/is_integral.hpp
+++ b/include/boost/type_traits/is_integral.hpp
@@ -41,6 +41,8 @@ BOOST_TT_AUX_BOOL_TRAIT_CV_SPEC1(is_integral,char,true)
 BOOST_TT_AUX_BOOL_TRAIT_CV_SPEC1(is_integral,wchar_t,true)
 #endif
 
+// Same set of integral types as in boost/type_traits/integral_promotion.hpp.
+// Please, keep in sync. -- Alexander Nasonov
 #if (defined(BOOST_MSVC) && (BOOST_MSVC < 1300)) \
     || (defined(BOOST_INTEL_CXX_VERSION) && defined(_MSC_VER) && (BOOST_INTEL_CXX_VERSION <= 600)) \
     || (defined(__BORLANDC__) && (__BORLANDC__ == 0x600) && (_MSC_VER < 1300))