Hi, Several places in Boost try to detect BOOST_OLD_IOSTREAMS using the following ifdefs: // support for pre 3.0 libstdc++ - thanks Phil Edwards! #if defined (__STL_CONFIG_H) && !defined (__STL_USE_NEW_IOSTREAMS) # define BOOST_OLD_IOSTREAMS #endif This incorrectly defines BOOST_OLD_IOSTREAMS for the Cray X1 C++ compiler. Could this be changed to include an && !defined(__crayx1) or something similar as in: #if defined (__STL_CONFIG_H) && !defined (__STL_USE_NEW_IOSTREAMS) && !defined(__crayx1) # define BOOST_OLD_IOSTREAMS #endif Three offending files are: boost/dynamic_bitset/config.hpp boost/range/iterator_range.hpp libs/dynamic_bitset/example/timing_tests.cpp Maybe it would be best to move this to the global config file? Best regards Matthias