diff --git a/include/boost/python/object/make_ptr_instance.hpp b/include/boost/python/object/make_ptr_instance.hpp
index 9bc9e86b..169106f4 100644
--- a/include/boost/python/object/make_ptr_instance.hpp
+++ b/include/boost/python/object/make_ptr_instance.hpp
@@ -35,7 +35,7 @@ struct make_ptr_instance
     static inline PyTypeObject* get_class_object_impl(U const volatile* p)
     {
 		if (p == 0)
-			return 0;
+			return 0; // means "return None".
 
         PyTypeObject* derived = get_derived_class_object(
             BOOST_DEDUCED_TYPENAME is_polymorphic<U>::type(), p);