scbarg.obj : error LNK2005: "struct unbounded_type::boost::detail::unbounded_type & boost::indexed_sets::`anonymous namespace'::unbounded" (?unbounded@?A0x65131fae@indexed_sets@boost@@3AAUunbounded_type@detail@23@A) already defined in scbarcf.obj scbarg.obj : error LNK2005: "struct unbounded_type::boost::detail::unbounded_type boost::indexed_sets::`anonymous namespace'::unbounded_obj" (?unbounded_obj@?A0x65131fae@indexed_sets@boost@@3Uunbounded_type@detail@23@A) already defined in scbarcf.obj Compiler is VC7.1 The two modules in the error messages don't use indexed_set at all but indexed_set.hpp is included globally. It seems as if indexed_set.hpp has a definition hiding in it somewhere. Here are the two declarations that appear in my project (they are in different namespaces so m_events_t does not collide): typedef is::indexed_set< event_t, is::index_list< is::unique >, is::non_unique >, is::non_unique ,&event_t::notepos>, notepos_compare> > > m_events_t; typedef is::indexed_set< event_t, is::index_list< is::unique >, is::non_unique >, is::non_unique > > > m_events_t; -- Using Opera's revolutionary e-mail client: http://www.opera.com/m2/