+;;; ANSI got UNSIGNED-BYTE wrong, prohibiting (UNSIGNED-BYTE 0).
+;;; Since this is actually a substantial impediment to clarity...
+(sb!xc:deftype unsigned-byte* (&optional s)
+ (cond
+ ((eq s '*) '(integer 0))
+ ((zerop s) '(integer 0 0))
+ (t `(unsigned-byte ,s))))
+