diff --git a/include/boost/type_traits/is_signed.hpp b/include/boost/type_traits/is_signed.hpp
index b283b21..b668313 100644
--- a/include/boost/type_traits/is_signed.hpp
+++ b/include/boost/type_traits/is_signed.hpp
@@ -13,6 +13,7 @@
 #include <boost/type_traits/is_integral.hpp>
 #include <boost/type_traits/remove_cv.hpp>
 #include <boost/type_traits/is_enum.hpp>
+#include <climits>
 
 namespace boost {
 
@@ -129,7 +130,8 @@ template <> struct is_signed<const ::boost::ulong_long_type> : public false_type
 template <> struct is_signed<volatile ::boost::ulong_long_type> : public false_type{};
 template <> struct is_signed<const volatile ::boost::ulong_long_type> : public false_type{};
 #endif
-#if defined(CHAR_MIN) && (CHAR_MIN != 0)
+#if defined(CHAR_MIN) 
+#if CHAR_MIN != 0
 template <> struct is_signed<char> : public true_type{};
 template <> struct is_signed<const char> : public true_type{};
 template <> struct is_signed<volatile char> : public true_type{};
@@ -140,8 +142,9 @@ template <> struct is_signed<const char> : public false_type{};
 template <> struct is_signed<volatile char> : public false_type{};
 template <> struct is_signed<const volatile char> : public false_type{};
 #endif
-#ifndef BOOST_NO_INTRINSIC_WCHAR_T
-#if defined(WCHAR_MIN) && (WCHAR_MIN != 0)
+#endif
+#if defined(WCHAR_MIN) && !defined(BOOST_NO_INTRINSIC_WCHAR_T)
+#if WCHAR_MIN != 0
 template <> struct is_signed<wchar_t> : public true_type{};
 template <> struct is_signed<const wchar_t> : public true_type{};
 template <> struct is_signed<volatile wchar_t> : public true_type{};
diff --git a/include/boost/type_traits/is_unsigned.hpp b/include/boost/type_traits/is_unsigned.hpp
index 7243771..8e83a33 100644
--- a/include/boost/type_traits/is_unsigned.hpp
+++ b/include/boost/type_traits/is_unsigned.hpp
@@ -14,6 +14,8 @@
 #include <boost/type_traits/is_enum.hpp>
 #include <boost/type_traits/remove_cv.hpp>
 
+#include <climits>
+
 namespace boost {
 
 #if !defined( __CODEGEARC__ )
@@ -128,7 +130,8 @@ template <> struct is_unsigned<const ::boost::long_long_type> : public false_typ
 template <> struct is_unsigned<volatile ::boost::long_long_type> : public false_type{};
 template <> struct is_unsigned<const volatile ::boost::long_long_type> : public false_type{};
 #endif
-#if defined(CHAR_MIN) && (CHAR_MIN == 0)
+#if defined(CHAR_MIN) 
+#if CHAR_MIN == 0
 template <> struct is_unsigned<char> : public true_type{};
 template <> struct is_unsigned<const char> : public true_type{};
 template <> struct is_unsigned<volatile char> : public true_type{};
@@ -139,8 +142,9 @@ template <> struct is_unsigned<const char> : public false_type{};
 template <> struct is_unsigned<volatile char> : public false_type{};
 template <> struct is_unsigned<const volatile char> : public false_type{};
 #endif
-#ifndef BOOST_NO_INTRINSIC_WCHAR_T
-#if defined(WCHAR_MIN) && (WCHAR_MIN == 0) && !defined(BOOST_NO_INTRINSIC_WCHAR_T)
+#endif
+#if !defined(BOOST_NO_INTRINSIC_WCHAR_T) && defined(WCHAR_MIN)
+#if WCHAR_MIN == 0
 template <> struct is_unsigned<wchar_t> : public true_type{};
 template <> struct is_unsigned<const wchar_t> : public true_type{};
 template <> struct is_unsigned<volatile wchar_t> : public true_type{};
diff --git a/test/is_signed_test.cpp b/test/is_signed_test.cpp
index c76a97a..66b7e15 100644
--- a/test/is_signed_test.cpp
+++ b/test/is_signed_test.cpp
@@ -12,6 +12,8 @@
 #  include <boost/type_traits/is_signed.hpp>
 #endif
 
+#include <climits>
+
 TT_TEST_BEGIN(is_signed)
 
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<int>::value, true);
@@ -35,6 +37,24 @@ BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<int[2]>::value, false);
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<boost::int128_type>::value, true);
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<boost::uint128_type>::value, false);
 #endif
+
+#if defined(CHAR_MIN)
+#if CHAR_MIN != 0
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<char>::value, true);
+#else
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<char>::value, false);
+#endif
+#endif
+
+
+#if defined(WCHAR_MIN)
+#if WCHAR_MIN != 0
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<wchar_t>::value, true);
+#else
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_signed<wchar_t>::value, false);
+#endif
+#endif
+
 TT_TEST_END
 
 
diff --git a/test/is_unsigned_test.cpp b/test/is_unsigned_test.cpp
index 484c11e..4323247 100644
--- a/test/is_unsigned_test.cpp
+++ b/test/is_unsigned_test.cpp
@@ -12,6 +12,8 @@
 #  include <boost/type_traits/is_unsigned.hpp>
 #endif
 
+#include <climits>
+
 TT_TEST_BEGIN(is_signed)
 
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<int>::value, false);
@@ -36,6 +38,23 @@ BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<boost::int128_type>::value, fals
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<boost::uint128_type>::value, true);
 #endif
 
+#if defined(CHAR_MIN)
+#if CHAR_MIN != 0
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<char>::value, false);
+#else
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<char>::value, true);
+#endif
+#endif
+
+
+#if defined(WCHAR_MIN)
+#if WCHAR_MIN != 0
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<wchar_t>::value, false);
+#else
+BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_unsigned<wchar_t>::value, true);
+#endif
+#endif
+
 TT_TEST_END