ICL seems not to handle sets that contain the maximum element of the domain type. I sent a similar mail a day ago, but I've simplified my example. Here's the code: Windows 7 Boost 1.59.0 ----BEGIN CODE--- using namespace std; typedef boost::icl::closed_interval<boost::uint16_t, std::less> interval_t; typedef boost::icl::split_interval_set<boost::uint16_t, std::less, interval_t> set_t; set_t s; s += interval_t(0x0000, 0xffff); s += interval_t(0xa000, 0xbfff); cout << "BAD: " << hex << s << endl; s.clear(); s += interval_t(0x0000, 0xfffe); s += interval_t(0xa000, 0xbfff); cout << "GOOD: " << hex << s << endl; ----END CODE--- ---BEGIN OUTPUT--- BAD: {[0,9fff][a000,ffff]} GOOD: {[0,9fff][a000,bfff][c000,fffe]} ---END OUTPUT--- The bad example seems to fail because the set contains 0xffff. In the good example I use 0xfffe.