I have graph as follows: struct cfg_node { iCode *ic; operand_map_t operands; std::set<var_t> alive; std::set<var_t> dying; }; typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, cfg_node> cfg_t; And a fragment of code: wassertl (!boost::num_vertices(cfg), "CFG non-empty before creation."); for (ic = start_ic, i = 0, j = 0; ic; ic = ic->next, i++) { boost::add_vertex(cfg); wassertl (cfg[i].alive.empty(), "Alive set non-empty upon creation."); Nothing inside the loop add or deletes vertices or changes the alive members. The code works fine on Linux, but I got bug reports from Windows users. For them the assertion in the loop triggers (and an attempt to insert something into alive later segfaults). So I have two questions: What could be the cause of this problem? Has it been encountered before? Is the approach of using cfg[i] to get the vertex still correct? I've used this for some time, but I can't find it in current boost documentation. Philipp