If I try to compile and load a file that's already compiled in Clozure, say doing this twice: (swank:compile-file-if-needed "/Users/ddp/src/lisp/test.lisp" t) On the second time around, swank signals an error in swank:collect- notes because Clozure returns a pathname of the fasl file instead of T. Clozure's behavior seems rational. So since the underlying defstruct specifies :type boolean for successp, here's how I fixed this: fluffy% diff -n swank.lisp.~1.671.~ swank.lisp d2786 2 a2787 2 (let ((successp (if successp t nil))) (make-compilation-result (reverse notes) successp seconds))))) (defun collect-notes (function) (let ((notes '())) (multiple-value-bind (successp seconds) (handler-bind ((compiler-condition (lambda (c) (push (make-compiler-note c) notes)))) (measure-time-interval function)) (let ((successp (if successp t nil))) (make-compilation-result (reverse notes) successp seconds)))))