diff --git a/lisp/org-num.el b/lisp/org-num.el
index 4179d1205..4a57e6a9e 100644
--- a/lisp/org-num.el
+++ b/lisp/org-num.el
@@ -461,6 +461,7 @@ NUMBERING is a list of numbers."
    (org-num-mode
     (unless (derived-mode-p 'org-mode)
       (user-error "Cannot activate headline numbering outside Org mode"))
+    (org-num--clear)
     (setq org-num--numbering nil)
     (setq org-num--overlays (nreverse (org-num--number-region nil nil)))
     (add-hook 'after-change-functions #'org-num--verify nil t)