FYI there is a bug in ECL affecting bordeaux-threads-0.8.3. (ql:quickload :bordeaux-threads) (bt:make-thread (lambda ())) There is no problem when bordeaux-threads is compiled for the first time, however thereafter loading from fasls will result in Condition of type: BORDEAUX-MP-CONDITION There is no support for this method on this implementation. The relevant ECL bug is http://sourceforge.net/p/ecls/bugs/261/ This does not affect bordeaux-threads-0.8.2.