The CLHS page for ADJUST-ARRAY says: An error of type error is signaled if fill-pointer is supplied and non-nil but array has no fill pointer. However, ECL says: > (lisp-implementation-version) "0.9i" > "foo" "foo" > (array-has-fill-pointer-p *) NIL > (adjust-array ** 3 :fill-pointer t) "foo" > (array-has-fill-pointer-p *) T