The following example could not be compiled: ================================================================= #include <string> #include <boost/program_options.hpp> namespace po = boost::program_options; int main() { std::wstring test; po::options_description desc("Allowed options"); desc.add_options() ("test", po::wvalue<std::wstring>(&test)->default_value(L"value"), "description"); } ================================================================= It is due to wvalue::default_value tries to do lexical_cast<std::string>(std::wstring). Also I cannot change default_value to default_value("value") as soon as it accepts only something convertible to std::wstring. In other words it is impossible to specify default_value for wstring option.