diff --git a/include/boost/detail/sp_convertible.hpp b/include/boost/detail/sp_convertible.hpp
new file mode 100644
index 0000000..00463b3
--- /dev/null
+++ b/include/boost/detail/sp_convertible.hpp
@@ -0,0 +1,60 @@
+#ifndef BOOST_DETAIL_SP_CONVERTIBLE_HPP_INCLUDED
+#define BOOST_DETAIL_SP_CONVERTIBLE_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//  detail/sp_convertible.hpp
+//
+//  Copyright 2008 Peter Dimov
+//
+//  Distributed under 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 <boost/config.hpp>
+
+namespace boost
+{
+
+namespace detail
+{
+
+template< class Y, class T > struct sp_convertible
+{
+    typedef char (&yes) [1];
+    typedef char (&no)  [2];
+
+    static yes f( T* );
+    static no  f( ... );
+
+    enum _vt { value = sizeof( f( (Y*)0 ) ) == sizeof(yes) };
+};
+
+struct sp_empty
+{
+};
+
+template< bool > struct sp_enable_if_convertible_impl;
+
+template<> struct sp_enable_if_convertible_impl<true>
+{
+    typedef sp_empty type;
+};
+
+template<> struct sp_enable_if_convertible_impl<false>
+{
+};
+
+template< class Y, class T > struct sp_enable_if_convertible: public sp_enable_if_convertible_impl< sp_convertible< Y, T >::value >
+{
+};
+
+} // namespace detail
+
+} // namespace boost
+
+#endif  // #ifndef BOOST_DETAIL_SP_TYPEINFO_HPP_INCLUDED
diff --git a/include/boost/intrusive_ptr.hpp b/include/boost/intrusive_ptr.hpp
index c4ec407..ace808b 100644
--- a/include/boost/intrusive_ptr.hpp
+++ b/include/boost/intrusive_ptr.hpp
@@ -23,8 +23,19 @@
 #include <boost/assert.hpp>
 #include <boost/detail/workaround.hpp>
 
+#if !defined( BOOST_NO_SFINAE )
+#include <boost/detail/sp_convertible.hpp>
+#endif
+
 #include <functional>           // for std::less
+
+#if !defined(BOOST_NO_IOSTREAM)
+#if !defined(BOOST_NO_IOSFWD)
 #include <iosfwd>               // for std::basic_ostream
+#else
+#include <ostream>
+#endif
+#endif
 
 
 namespace boost
@@ -66,9 +77,19 @@ public:
 
 #if !defined(BOOST_NO_MEMBER_TEMPLATES) || defined(BOOST_MSVC6_MEMBER_TEMPLATES)
 
-    template<class U> intrusive_ptr(intrusive_ptr<U> const & rhs): p_(rhs.get())
+    template<class U>
+#if !defined( BOOST_NO_SFINAE )
+
+    intrusive_ptr( intrusive_ptr<U> const & rhs, typename detail::sp_enable_if_convertible<U,T>::type = detail::sp_empty() )
+
+#else
+
+    intrusive_ptr( intrusive_ptr<U> const & rhs )
+
+#endif
+    : p_( rhs.get() )
     {
-        if(p_ != 0) intrusive_ptr_add_ref(p_);
+        if( p_ != 0 ) intrusive_ptr_add_ref( p_ );
     }
 
 #endif
@@ -246,7 +267,9 @@ template<class T, class U> intrusive_ptr<T> dynamic_pointer_cast(intrusive_ptr<U
 
 // operator<<
 
-#if defined(__GNUC__) &&  (__GNUC__ < 3)
+#if !defined(BOOST_NO_IOSTREAM)
+
+#if defined(BOOST_NO_TEMPLATED_IOSTREAMS) || ( defined(__GNUC__) &&  (__GNUC__ < 3) )
 
 template<class Y> std::ostream & operator<< (std::ostream & os, intrusive_ptr<Y> const & p)
 {
@@ -275,6 +298,8 @@ template<class E, class T, class Y> std::basic_ostream<E, T> & operator<< (std::
 
 #endif // __GNUC__ < 3
 
+#endif // !defined(BOOST_NO_IOSTREAM)
+
 } // namespace boost
 
 #ifdef BOOST_MSVC
diff --git a/include/boost/shared_ptr.hpp b/include/boost/shared_ptr.hpp
index 9256351..7245cac 100644
--- a/include/boost/shared_ptr.hpp
+++ b/include/boost/shared_ptr.hpp
@@ -32,6 +32,10 @@
 #include <boost/detail/shared_count.hpp>
 #include <boost/detail/workaround.hpp>
 
+#if !defined( BOOST_NO_SFINAE )
+#include <boost/detail/sp_convertible.hpp>
+#endif
+
 #if !defined(BOOST_SP_NO_ATOMIC_ACCESS)
 #include <boost/detail/spinlock_pool.hpp>
 #include <boost/memory_order.hpp>
@@ -224,11 +228,20 @@ public:
     }
 
     template<class Y>
-    shared_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+#if !defined( BOOST_NO_SFINAE )
+
+    shared_ptr( shared_ptr<Y> const & r, typename detail::sp_enable_if_convertible<Y,T>::type = detail::sp_empty() )
+
+#else
+
+    shared_ptr( shared_ptr<Y> const & r )
+
+#endif
+    : px( r.px ), pn( r.pn ) // never throws
     {
     }
 
-    shared_ptr(detail::shared_count const & c, T * p): px(p), pn(c) // never throws
+    shared_ptr( detail::shared_count const & c, T * p ): px( p ), pn( c ) // never throws
     {
     }
 
diff --git a/include/boost/weak_ptr.hpp b/include/boost/weak_ptr.hpp
index 4335738..aadb60a 100644
--- a/include/boost/weak_ptr.hpp
+++ b/include/boost/weak_ptr.hpp
@@ -61,13 +61,31 @@ public:
 //
 
     template<class Y>
-    weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws
+#if !defined( BOOST_NO_SFINAE )
+
+    weak_ptr( weak_ptr<Y> const & r, typename detail::sp_enable_if_convertible<Y,T>::type = detail::sp_empty() )
+
+#else
+
+    weak_ptr( weak_ptr<Y> const & r )
+
+#endif
+    : pn(r.pn) // never throws
     {
         px = r.lock().get();
     }
 
     template<class Y>
-    weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+#if !defined( BOOST_NO_SFINAE )
+
+    weak_ptr( shared_ptr<Y> const & r, typename detail::sp_enable_if_convertible<Y,T>::type = detail::sp_empty() )
+
+#else
+
+    weak_ptr( shared_ptr<Y> const & r )
+
+#endif
+    : px( r.px ), pn( r.pn ) // never throws
     {
     }
 
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 86d0289..3e10e73 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -46,5 +46,8 @@ import testing ;
           [ run sp_accept_owner_test.cpp ]
           [ run sp_atomic_test.cpp ]
           [ run make_shared_test.cpp ]
+          [ run sp_convertible_test.cpp ]
+          [ run wp_convertible_test.cpp ]
+          [ run ip_convertible_test.cpp ]
         ;
 }
diff --git a/test/ip_convertible_test.cpp b/test/ip_convertible_test.cpp
new file mode 100644
index 0000000..081f7b0
--- /dev/null
+++ b/test/ip_convertible_test.cpp
@@ -0,0 +1,54 @@
+#include <boost/config.hpp>
+
+//  wp_convertible_test.cpp
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under 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 <boost/detail/lightweight_test.hpp>
+#include <boost/intrusive_ptr.hpp>
+
+//
+
+struct W
+{
+};
+
+void intrusive_ptr_add_ref( W* )
+{
+}
+
+void intrusive_ptr_release( W* )
+{
+}
+
+struct X: public virtual W
+{
+};
+
+struct Y: public virtual W
+{
+};
+
+struct Z: public X
+{
+};
+
+int f( boost::intrusive_ptr<X> )
+{
+    return 1;
+}
+
+int f( boost::intrusive_ptr<Y> )
+{
+    return 2;
+}
+
+int main()
+{
+    BOOST_TEST( 1 == f( boost::intrusive_ptr<Z>() ) );
+    return boost::report_errors();
+}
diff --git a/test/sp_convertible_test.cpp b/test/sp_convertible_test.cpp
new file mode 100644
index 0000000..165d55f
--- /dev/null
+++ b/test/sp_convertible_test.cpp
@@ -0,0 +1,66 @@
+#include <boost/config.hpp>
+
+//  sp_convertible_test.cpp
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under 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 <boost/detail/lightweight_test.hpp>
+#include <boost/shared_ptr.hpp>
+
+//
+
+class incomplete;
+
+struct X
+{
+};
+
+struct Y
+{
+};
+
+struct Z: public X
+{
+};
+
+int f( boost::shared_ptr<void const> )
+{
+    return 1;
+}
+
+int f( boost::shared_ptr<int> )
+{
+    return 2;
+}
+
+int f( boost::shared_ptr<incomplete> )
+{
+    return 3;
+}
+
+int g( boost::shared_ptr<X> )
+{
+    return 4;
+}
+
+int g( boost::shared_ptr<Y> )
+{
+    return 5;
+}
+
+int g( boost::shared_ptr<incomplete> )
+{
+    return 6;
+}
+
+int main()
+{
+    BOOST_TEST( 1 == f( boost::shared_ptr<double>() ) );
+    BOOST_TEST( 4 == g( boost::shared_ptr<Z>() ) );
+
+    return boost::report_errors();
+}
diff --git a/test/wp_convertible_test.cpp b/test/wp_convertible_test.cpp
new file mode 100644
index 0000000..cceacda
--- /dev/null
+++ b/test/wp_convertible_test.cpp
@@ -0,0 +1,68 @@
+#include <boost/config.hpp>
+
+//  wp_convertible_test.cpp
+//
+//  Copyright (c) 2008 Peter Dimov
+//
+//  Distributed under 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 <boost/detail/lightweight_test.hpp>
+#include <boost/weak_ptr.hpp>
+
+//
+
+class incomplete;
+
+struct X
+{
+};
+
+struct Y
+{
+};
+
+struct Z: public X
+{
+};
+
+int f( boost::weak_ptr<void const> )
+{
+    return 1;
+}
+
+int f( boost::weak_ptr<int> )
+{
+    return 2;
+}
+
+int f( boost::weak_ptr<incomplete> )
+{
+    return 3;
+}
+
+int g( boost::weak_ptr<X> )
+{
+    return 4;
+}
+
+int g( boost::weak_ptr<Y> )
+{
+    return 5;
+}
+
+int g( boost::weak_ptr<incomplete> )
+{
+    return 6;
+}
+
+int main()
+{
+    BOOST_TEST( 1 == f( boost::weak_ptr<double>() ) );
+    BOOST_TEST( 1 == f( boost::shared_ptr<double>() ) );
+    BOOST_TEST( 4 == g( boost::weak_ptr<Z>() ) );
+    BOOST_TEST( 4 == g( boost::shared_ptr<Z>() ) );
+
+    return boost::report_errors();
+}