X-Debbugs-Cc: Stefan Monnier [ CC to Stefan, who seems to be the original author of that cookie handling thingy ... apologies if that does not really concern you ] Variable `url-cookie-save-interval' can be perfectly well configured to nil, as one can see in function `url-cookie-setup-save-timer' (which seems to be the only function referencing that variable): (defun url-cookie-setup-save-timer () "Reset the cookie saver timer." (interactive) (ignore-errors (cancel-timer url-cookie-timer)) (setq url-cookie-timer nil) (if url-cookie-save-interval (setq url-cookie-timer (run-at-time url-cookie-save-interval url-cookie-save-interval #'url-cookie-write-file)))) However, the docstring and the :type of the defcustom do not document/allow for nil as a valid value. The attached patch fixes that, please check. Thanks!