diff --git a/README.org b/README.org
index 3826f95..8029b26 100644
--- a/README.org
+++ b/README.org
@@ -2594,9 +2594,9 @@ Listing [[lst:configure-format-all]]:
     (add-hook 'org-babel-post-tangle-hook
               (defun format-all-org-babel-post-tangle ()
                 (when (derived-mode-p 'python-mode)
-                  (let ((format-all-formatters '(("Python" black))))
-                    (message "Format whole `%s' buffer after tangling" major-mode)
-                    (format-all-buffer))))))
+                  (setq-local format-all-formatters '(("Python" black)))
+                  (message "Format whole `%s' buffer after tangling" major-mode)
+                  (format-all-buffer)))))
 #+end_src
 
 ** [[https://dept-info.labri.fr/~strandh/Teaching/PFS/Common/Strandh-Tutorial/Dir-symbolic.html][Common Lisp programming]]