Symbol *default-special-bindings* is exported and documented, but it does not appear to be implemented max@momoland:~/lisp-systems/bordeaux-threads_0.5.0> grep -i default-special **/* src/bordeaux-threads.lisp: #:*default-special-bindings* #:*supports-threads-p* src/bordeaux-threads.lisp:(defvar *default-special-bindings* '() Should not the make-thread function massage them and do (progv ...)? Regards, Max