I did the following (probably stupid) set of commands: HEAP-PACKAGE> (setq h '(1 2 3)) (1 2 3) HEAP-PACKAGE> (setf (last h) nil) ;Compiler warnings : ; Undeclared free variable H, in an anonymous lambda form. ; Undefined function SETF::|COMMON-LISP::LAST|, in an anonymous lambda form. Is that a bug? -a