The Supreme Election Council (YSK) said mid-Sunday that ballots without authenticating stamps will be considered valid unless proven to have been brought from outside the polling station.
Turks are voting on whether to shift from a parliamentary system of governance to an executive presidency that is expected to give sweeping powers to President Recep Tayyip Erdoğan.
Polling stations throughout Turkey were closed at 5 p.m. on Sunday.
