Is it permissible to fold the corners of the Mus'haf's pages to mark stopping places?

A reader of the Quran should not fold the corner of a page. It is better to use a bookmark or the Quran's string marker at the point where they stop. Ibn Hajar al-Haytami stated that one should mark the place with a piece of paper, not with a stick or by folding the corner of the page.