diff --git a/include/boost/type_traits/is_abstract.hpp b/include/boost/type_traits/is_abstract.hpp
index 15d4afe..a11718d 100644
--- a/include/boost/type_traits/is_abstract.hpp
+++ b/include/boost/type_traits/is_abstract.hpp
@@ -92,13 +92,13 @@ struct is_abstract_imp2
    // GCC2 won't even parse this template if we embed the computation
    // of s1 in the computation of value.
 #ifdef __GNUC__
-   BOOST_STATIC_CONSTANT(unsigned, s1 = sizeof(is_abstract_imp2<T>::template check_sig<T>(0)));
+   BOOST_STATIC_CONSTANT(std::size_t, s1 = sizeof(is_abstract_imp2<T>::template check_sig<T>(0)));
 #else
 #if BOOST_WORKAROUND(_MSC_FULL_VER, >= 140050000)
 #pragma warning(push)
 #pragma warning(disable:6334)
 #endif
-   BOOST_STATIC_CONSTANT(unsigned, s1 = sizeof(check_sig<T>(0)));
+   BOOST_STATIC_CONSTANT(std::size_t, s1 = sizeof(check_sig<T>(0)));
 #if BOOST_WORKAROUND(_MSC_FULL_VER, >= 140050000)
 #pragma warning(pop)
 #endif
diff --git a/include/boost/type_traits/is_virtual_base_of.hpp b/include/boost/type_traits/is_virtual_base_of.hpp
new file mode 100644
index 0000000..74cbe4e
--- /dev/null
+++ b/include/boost/type_traits/is_virtual_base_of.hpp
@@ -0,0 +1,87 @@
+//  (C) Copyright Daniel Frey and Robert Ramey 2009.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/type_traits for most recent version including documentation.
+ 
+#ifndef BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED
+#define BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED
+
+#include <boost/type_traits/is_base_of.hpp>
+#include <boost/type_traits/is_same.hpp>
+#include <boost/mpl/and.hpp>
+#include <boost/mpl/not.hpp>
+
+// should be the last #include
+#include <boost/type_traits/detail/bool_trait_def.hpp>
+
+namespace boost {
+namespace detail {
+
+
+#ifdef BOOST_MSVC
+#pragma warning( push )
+#pragma warning( disable : 4584 )
+#elif defined __GNUC__
+#pragma GCC system_header
+#endif
+
+template<typename Base, typename Derived, typename tag>
+struct is_virtual_base_of_impl
+{
+    BOOST_STATIC_CONSTANT(bool, value = false);
+};
+
+template<typename Base, typename Derived>
+struct is_virtual_base_of_impl<Base, Derived, mpl::true_>
+{
+    struct X : Derived, virtual Base 
+    {
+       X();
+       X(const X&);
+       X& operator=(const X&);
+       ~X();
+    };
+    struct Y : Derived 
+    {
+       Y();
+       Y(const Y&);
+       Y& operator=(const Y&);
+       ~Y();
+    };
+    BOOST_STATIC_CONSTANT(bool, value = sizeof(X)==sizeof(Y));
+};
+
+template<typename Base, typename Derived>
+struct is_virtual_base_of_impl2
+{
+   typedef typename mpl::and_<is_base_of<Base, Derived>, mpl::not_<is_same<Base, Derived> > >::type tag_type;
+   typedef is_virtual_base_of_impl<Base, Derived, tag_type> imp;
+   BOOST_STATIC_CONSTANT(bool, value = imp::value);
+};
+
+#ifdef BOOST_MSVC
+#pragma warning( pop )
+#endif
+
+} // namespace detail
+
+BOOST_TT_AUX_BOOL_TRAIT_DEF2(
+      is_virtual_base_of
+       , Base
+       , Derived
+       , (::boost::detail::is_virtual_base_of_impl2<Base,Derived>::value) 
+)
+
+#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_virtual_base_of,Base&,Derived,false)
+BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_virtual_base_of,Base,Derived&,false)
+BOOST_TT_AUX_BOOL_TRAIT_PARTIAL_SPEC2_2(typename Base,typename Derived,is_virtual_base_of,Base&,Derived&,false)
+#endif
+
+} // namespace boost
+
+#include <boost/type_traits/detail/bool_trait_undef.hpp>
+
+#endif
diff --git a/test/is_base_of_test.cpp b/test/is_base_of_test.cpp
old mode 100755
new mode 100644
index 97d29c1..6817ffb
--- a/test/is_base_of_test.cpp
+++ b/test/is_base_of_test.cpp
@@ -36,6 +36,8 @@ BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_base_of<VB,VD>::value), true);
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_base_of<VD,VB>::value), false);
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_base_of<test_abc1,test_abc3>::value), true);
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_base_of<test_abc3,test_abc1>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_base_of<Base,virtual_inherit1>::value), true);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_base_of<virtual_inherit1,Base>::value), false);
 
 TT_TEST_END
 
diff --git a/test/is_virtual_base_of_test.cpp b/test/is_virtual_base_of_test.cpp
new file mode 100644
index 0000000..6c3dc2a
--- /dev/null
+++ b/test/is_virtual_base_of_test.cpp
@@ -0,0 +1,54 @@
+
+//  (C) Copyright John Maddock 2009. 
+//  Use, modification and distribution are subject to the 
+//  Boost Software License, Version 1.0. (See accompanying file 
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+#include "test.hpp"
+#include "check_integral_constant.hpp"
+#include <boost/type_traits/is_virtual_base_of.hpp>
+
+
+TT_TEST_BEGIN(is_virtual_base_of)
+
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Derived,Base>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Derived,Derived>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,Base>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,Derived>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,MultiBase>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Derived,MultiBase>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Derived2,MultiBase>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,PrivateBase>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<NonDerived,Base>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,void>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,const void>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<void,Derived>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<const void,Derived>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<int, int>::value), false);  // really it is!!!!!
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<const int, int>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<VB,VD>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<VD,VB>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<test_abc1,test_abc3>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<test_abc3,test_abc1>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,virtual_inherit1>::value), true);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<virtual_inherit1,Base>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,virtual_inherit2>::value), true);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<virtual_inherit2,Base>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<Base,virtual_inherit3>::value), true);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<virtual_inherit3,Base>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<boost::noncopyable,virtual_inherit4>::value), true);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<virtual_inherit4,boost::noncopyable>::value), false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<int_convertible,virtual_inherit5>::value), true);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<virtual_inherit5,int_convertible>::value), false);
+
+TT_TEST_END
+
+
+
+
+
+
+
+
+
diff --git a/test/test.hpp b/test/test.hpp
index 2e354b9..972441b 100644
--- a/test/test.hpp
+++ b/test/test.hpp
@@ -367,8 +367,9 @@ struct polymorphic_derived2 : polymorphic_base
 
 struct virtual_inherit1 : virtual Base { };
 struct virtual_inherit2 : virtual_inherit1 { };
-
-
+struct virtual_inherit3 : private virtual Base {};
+struct virtual_inherit4 : private virtual boost::noncopyable {};
+struct virtual_inherit5 : private virtual int_convertible {};
 
 typedef void foo0_t();
 typedef void foo1_t(int);