Hi, Erik When I try to compile recent usocket trunk code, two issues found: In condition.lisp, the (define-condition insufficient-implementation) cannot compiled on LispWorks: **++++ Error in (SUBFUNCTION (DEFCLASS USOCKET:INSUFFICIENT-IMPLEMENTATION) (DEFINE-CONDITION USOCKET:INSUFFICIENT- IMPLEMENTATION)): FUNCTION is defined as an ordinary function #<Function SYSTEM::UNDEFINED-FEXPR-FUNCTION 20259C4A> I checked CLHS ( http://www.lispworks.com/documentation/HyperSpec/Body/s_fn.htm ), it says FUNCTION is a "Special Operator" which serves as a function: (defun adder (x) (function (lambda (y) (+ x y)))) (setq add3 (adder 3)) (funcall add3 5) => 8 So you define it into a slot reader will cause symbol conflict with Common Lisp itself. LispWorks is quite strict, other CLs just pass it. I suggest you use FUNCTION-OF instead of FUNCTION, like this: (define-condition insufficient-implementation (error) ((feature :initarg :feature :reader feature) (function :initarg :function :reader function-of)) (:documentation "The ancestor of all errors usocket may generate because of insufficient support from the underlying implementation with respect to the arguments given to `function'. One call may signal several errors, if the caller allows processing to continue. ")) With this change, I can compile and load on LispWorks now. But I don't know where else you use this reader function. Please review this, and make some change for LispWorks. Thanks, --binghe