diff --git a/include/boost/smart_ptr/detail/shared_count.hpp b/include/boost/smart_ptr/detail/shared_count.hpp
index 69cc915..85e6b1f 100644
--- a/include/boost/smart_ptr/detail/shared_count.hpp
+++ b/include/boost/smart_ptr/detail/shared_count.hpp
@@ -494,11 +494,13 @@ public:
         return a.pi_ == b.pi_;
     }
 
-    friend inline bool operator<(shared_count const & a, shared_count const & b) BOOST_SP_NOEXCEPT
+    bool operator<( shared_count const & r ) const BOOST_SP_NOEXCEPT
     {
-        return std::less<sp_counted_base *>()( a.pi_, b.pi_ );
+        return std::less<sp_counted_base *>()( pi_, r.pi_ );
     }
 
+    bool operator<( weak_count const & r ) const BOOST_SP_NOEXCEPT;
+
     void * get_deleter( sp_typeinfo_ const & ti ) const BOOST_SP_NOEXCEPT
     {
         return pi_? pi_->get_deleter( ti ): 0;
@@ -625,9 +627,14 @@ public:
         return a.pi_ == b.pi_;
     }
 
-    friend inline bool operator<(weak_count const & a, weak_count const & b) BOOST_SP_NOEXCEPT
+    bool operator<( weak_count const & r ) const BOOST_SP_NOEXCEPT
     {
-        return std::less<sp_counted_base *>()(a.pi_, b.pi_);
+        return std::less<sp_counted_base *>()( pi_, r.pi_ );
+    }
+
+    bool operator<( shared_count const & r ) const BOOST_SP_NOEXCEPT
+    {
+        return std::less<sp_counted_base *>()( pi_, r.pi_ );
     }
 };
 
@@ -653,6 +660,11 @@ inline shared_count::shared_count( weak_count const & r, sp_nothrow_tag ) BOOST_
     }
 }
 
+inline bool shared_count::operator<( weak_count const & r ) const BOOST_SP_NOEXCEPT
+{
+    return std::less<sp_counted_base *>()( pi_, r.pi_ );
+}
+
 } // namespace detail
 
 } // namespace boost