[Boost-users] Program options negative arguments

If I setup a multitoken option like this: desc.add_options() ("NumberList", po::value()->multitoken(), "List of numbers.") and then call the program with: ./Program --NumberList 1 2 -3 4 it treats the number "-3" as a new flag so it produces an "unknown option" error. Is there a way to handle this negative argument? Thanks, David