The result of the referendum that grants sweeping new powers to the president of Turkey is valid, the head of the electoral body says.
Sadi Guven was speaking after the main opposition Republican People's Party (CHP) cited irregularities, including the use of unstamped ballot papers.
President Recep Tayyip Erdogan's push for an executive presidency succeeded with just over 51% of the vote.
The win was met with both celebrations and protests across Turkey.
The CHP has demanded a recount of 60% of the votes.
But Mr Guven told reporters on Monday the unstamped ballot papers had been produced by the High Electoral Board and were valid.
I can't see this result being overturned without bloodshed. I hope I'm wrong but my opinion is that we are now heading for a strict Islamic dictatorship in Turkey under Erdogan. Stand by for another refugee crisis which is going to dwarf anything we've had so far.