Index: boost/enable_shared_from_this.hpp
===================================================================
--- boost/enable_shared_from_this.hpp	(revision 44373)
+++ boost/enable_shared_from_this.hpp	(working copy)
@@ -30,7 +30,8 @@
         if( !owned() && _internal_shared_this.get() == 0 )
         {
             T * p = dynamic_cast<T *>(const_cast<enable_shared_from_this*>(this));
-            _internal_shared_this = shared_ptr<T>( p, detail::sp_deleter_wrapper() );
+            detail::shared_count c(p, detail::sp_deleter_wrapper());
+            shared_ptr<T>(c, p).swap(_internal_shared_this);
             BOOST_ASSERT(_internal_shared_this.get() == this);
             _internal_weak_this = _internal_shared_this;
         }
@@ -125,10 +126,6 @@
     }
 }
 
-template< class T, class Y > inline void sp_accept_owner( boost::shared_ptr<Y> * /*ptr*/, boost::enable_shared_from_this<T> const * /*pe*/, boost::detail::sp_deleter_wrapper * /*pd*/ )
-{
-}
-
 } // namespace boost
 
 #endif  // #ifndef BOOST_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED
Index: boost/detail/shared_count.hpp
===================================================================
--- boost/detail/shared_count.hpp	(revision 44373)
+++ boost/detail/shared_count.hpp	(working copy)
@@ -25,7 +25,6 @@
 #include <boost/config.hpp>
 #include <boost/checked_delete.hpp>
 #include <boost/throw_exception.hpp>
-#include <boost/detail/bad_weak_ptr.hpp>
 #include <boost/detail/sp_counted_base.hpp>
 #include <boost/detail/sp_counted_impl.hpp>
 
@@ -46,8 +45,6 @@
 
 #endif
 
-struct sp_nothrow_tag {};
-
 class weak_count;
 
 class shared_count
@@ -217,8 +214,7 @@
         if( pi_ != 0 ) pi_->add_ref_copy();
     }
 
-    explicit shared_count(weak_count const & r); // throws bad_weak_ptr when r.use_count() == 0
-    shared_count( weak_count const & r, sp_nothrow_tag ); // constructs an empty *this when r.use_count() == 0
+    explicit shared_count(weak_count const & r); // nothrow
 
     shared_count & operator= (shared_count const & r) // nothrow
     {
@@ -366,17 +362,6 @@
         , id_(shared_count_id)
 #endif
 {
-    if( pi_ == 0 || !pi_->add_ref_lock() )
-    {
-        boost::throw_exception( boost::bad_weak_ptr() );
-    }
-}
-
-inline shared_count::shared_count( weak_count const & r, sp_nothrow_tag ): pi_( r.pi_ )
-#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
-        , id_(shared_count_id)
-#endif
-{
     if( pi_ != 0 && !pi_->add_ref_lock() )
     {
         pi_ = 0;
Index: boost/weak_ptr.hpp
===================================================================
--- boost/weak_ptr.hpp	(revision 44373)
+++ boost/weak_ptr.hpp	(working copy)
@@ -93,7 +93,8 @@
 
     shared_ptr<T> lock() const // never throws
     {
-        return shared_ptr<element_type>( *this, boost::detail::sp_nothrow_tag() );
+        detail::shared_count c(pn);
+        return shared_ptr<T>(c, !c.empty() ? px : 0);
     }
 
     long use_count() const // never throws
Index: boost/shared_ptr.hpp
===================================================================
--- boost/shared_ptr.hpp	(revision 44373)
+++ boost/shared_ptr.hpp	(working copy)
@@ -25,6 +25,7 @@
 #include <boost/assert.hpp>
 #include <boost/checked_delete.hpp>
 #include <boost/throw_exception.hpp>
+#include <boost/detail/bad_weak_ptr.hpp>
 #include <boost/detail/shared_count.hpp>
 #include <boost/detail/workaround.hpp>
 
@@ -199,19 +200,19 @@
 #endif
 
     template<class Y>
-    explicit shared_ptr(weak_ptr<Y> const & r): pn(r.pn) // may throw
+    explicit shared_ptr(weak_ptr<Y> const & r): pn(r.pn)
     {
-        // it is now safe to copy r.px, as pn(r.pn) did not throw
+        if( pn.empty() )
+            boost::throw_exception( boost::bad_weak_ptr() );
+
+        // it is now safe to copy r.px, as pn is not empty
         px = r.px;
     }
 
     template<class Y>
-    shared_ptr( weak_ptr<Y> const & r, boost::detail::sp_nothrow_tag ): px( 0 ), pn( r.pn, boost::detail::sp_nothrow_tag() ) // never throws
+    shared_ptr(detail::shared_count & c, Y * p): px(p) // never throws
     {
-        if( !pn.empty() )
-        {
-            px = r.px;
-        }
+        pn.swap(c);
     }
 
     template<class Y>
@@ -468,6 +469,11 @@
         return pn.get_deleter( ti );
     }
 
+    detail::shared_count const & _internal_shared_count() const // never throws
+    {
+        return pn;
+    }
+
 // Tasteless as this may seem, making all members public allows member templates
 // to work in the absence of member template friends. (Matthew Langston)