diff --git a/lisp/org-clock.el b/lisp/org-clock.el
index 321dd95..ce309ef 100644
--- a/lisp/org-clock.el
+++ b/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)