diff --git a/lisp/ox.el b/lisp/ox.el
index 00772033a..bc56414e4 100644
--- a/lisp/ox.el
+++ b/lisp/ox.el
@@ -3207,8 +3207,7 @@ locally for the subtree through node properties."
     (when options
       (let ((items
 	     (mapcar
-	      (lambda (opt)
-		(format "%s:%s" (car opt) (format "%s" (cdr opt))))
+	      #'(lambda (opt) (format "%s:%S" (car opt) (cdr opt)))
 	      (sort options (lambda (k1 k2) (string< (car k1) (car k2)))))))
 	(if subtreep
 	    (org-entry-put