The Defterdar Mosque, or in long form the Defterdar Mahmut Efendi Mosque (Turkish: Defterdar Camii, Defterdar Mahmut Efendi Camii), is a historical mosque located in Eyüp, Istanbul, Turkey. It was commissioned by DefterdarNazlı Mahmut Efendi (c. 1500-1546) and built by architect Mimar Sinan in 1542 ("defterdar" was the head of the financial department in Ottoman Empire). Instead of a crescent, this mosque has "ink pot and pen" on top of its dome, representing the profession of the founder of the mosque. (since "defterdar" means chamberlain, literally it means defter:notebook + dar:suffix for "doer"). The original pair was broken by a storm in 1997. Ten years later, on 30 May 2007, a new inkpot and a pen assembled on top of the dome of the mosque.