A high-energy double-crystal x-ray monochromator has been constructed for use on the X-17 beam line at the National Synchrotron Light Source (NSLS). Its design is based on the "boomerang" right angle linkage, and features a fixed exit beam, a cooled first crystal, and an energy range of 8-92 keV. The entire mechanism is UHV compatible. The design is described and performance details, obtained in testing at the X17 beam line, are presented.