Amend previous patch

lisp/org-clock.el

@@ -339,7 +339,7 @@ of a different task.")
 		    (if (< i 10)
 			(+ i ?0)
 		      (+ i (- ?A 10))) m))
-	   (if (fboundp 'int-to-char) (setq s (int-to-char s)))
+	   (if (fboundp 'int-to-char) (setf (car s) (int-to-char (car s))))
 	   (push s sel-list)))
        org-clock-history)
       (org-fit-window-to-buffer)