diff --git a/include/boost/type_traits/detail/has_binary_operator.hpp b/include/boost/type_traits/detail/has_binary_operator.hpp
index 8984a70..d439e8e 100644
--- a/include/boost/type_traits/detail/has_binary_operator.hpp
+++ b/include/boost/type_traits/detail/has_binary_operator.hpp
@@ -38,7 +38,7 @@
 // cannot find another implementation -> declared as system header to suppress these warnings.
 #if defined(__GNUC__) && ((__GNUC__==3 && __GNUC_MINOR__>=1) || (__GNUC__>3))
 #   pragma GCC system_header
-#elif BOOST_MSVC
+#elif defined(BOOST_MSVC)
 #   pragma warning ( push )
 #   pragma warning ( disable : 4018 4244 4547 4800 4804 4805 4913 )
 #endif
@@ -222,7 +222,7 @@ BOOST_TT_AUX_BOOL_TRAIT_DEF3(BOOST_TT_TRAIT_NAME, Lhs, Rhs=Lhs, Ret=::boost::det
 
 } // namespace boost
 
-#ifdef BOOST_MSVC
+#if defined(BOOST_MSVC)
 #   pragma warning ( pop )
 #endif
 
diff --git a/include/boost/type_traits/detail/has_postfix_operator.hpp b/include/boost/type_traits/detail/has_postfix_operator.hpp
index 79fdaf9..d50b3d5 100644
--- a/include/boost/type_traits/detail/has_postfix_operator.hpp
+++ b/include/boost/type_traits/detail/has_postfix_operator.hpp
@@ -21,9 +21,12 @@
 // should be the last #include
 #include <boost/type_traits/detail/bool_trait_def.hpp>
 
-#if defined(BOOST_MSVC)
+// avoid warnings
+#if defined(__GNUC__) && ((__GNUC__==3 && __GNUC_MINOR__>=1) || (__GNUC__>3))
+#   pragma GCC system_header
+#elif defined(BOOST_MSVC)
 #   pragma warning ( push )
-#   pragma warning ( disable : 4913 4244 )
+#   pragma warning ( disable : 4244 4913 )
 #endif
 
 namespace boost {
@@ -194,7 +197,7 @@ BOOST_TT_AUX_BOOL_TRAIT_DEF2(BOOST_TT_TRAIT_NAME, Lhs, Ret=::boost::detail::BOOS
 } // namespace boost
 
 #if defined(BOOST_MSVC)
-#   pragma warning (pop)
+#   pragma warning ( pop )
 #endif
 
 #include <boost/type_traits/detail/bool_trait_undef.hpp>
diff --git a/include/boost/type_traits/detail/has_prefix_operator.hpp b/include/boost/type_traits/detail/has_prefix_operator.hpp
index bdea27e..de80bbe 100644
--- a/include/boost/type_traits/detail/has_prefix_operator.hpp
+++ b/include/boost/type_traits/detail/has_prefix_operator.hpp
@@ -32,7 +32,7 @@
 // cannot find another implementation -> declared as system header to suppress these warnings.
 #if defined(__GNUC__) && ((__GNUC__==3 && __GNUC_MINOR__>=1) || (__GNUC__>3))
 #   pragma GCC system_header
-#elif BOOST_MSVC
+#elif defined(BOOST_MSVC)
 #   pragma warning ( push )
 #   pragma warning ( disable : 4146 4804 4913 4244 )
 #endif
@@ -203,7 +203,7 @@ BOOST_TT_AUX_BOOL_TRAIT_DEF2(BOOST_TT_TRAIT_NAME, Rhs, Ret=::boost::detail::BOOS
 
 } // namespace boost
 
-#ifdef BOOST_MSVC
+#if defined(BOOST_MSVC)
 #   pragma warning ( pop )
 #endif