A re-run of Austria's presidential election is likely to be postponed because the glue on postal voting forms won't stick.
Austrian media reported that postal voters had complained they were unable to seal their ballots properly.
Austria's Interior Ministry confirmed the problem had rendered some postal votes invalid.
The Green-supported candidate, Alexander Van der Bellen, won the presidential election in May by a margin of 0.6 percentage points, or 30,863 votes.
A re-run was ordered after Norbert Hofer's far-right Freedom Party challenged Mr Van der Bellen's narrow win.
The two candidates both said they no longer expected the election to be held on 2 October as planned.
Mr Van der Bellen told a news conference on Saturday that he was braced for a postponement. "I hope that [the election] can still take place this year," he said.
"The notion that someone posts a valid ballot paper abiding by all legal provisions, and then this valid vote then be declared invalid because the damn glue doesn't work - this notion is - ladies and gentlemen - intolerable."
His rival's campaign has been typical of the current rise of nationalism across Europe.
Mr Hofer told would-be voters: "To those in Austria who go to war for the Islamic State or rape women - I say to those people, 'This is not your home'."
Mr Van der Bellen, a former economics professor, campaigned against nationalist fervour.
"I've experienced how Austria rose from the ruins of World War Two, caused by the madness of nationalism."
The Austrian presidency is a mostly ceremonial post, but the president can dissolve the National Council - the more powerful lower house of parliament - triggering a general election.
The president can only do that once for a particular reason - they cannot use the same grounds to dissolve it again.
The chancellor appoints government ministers and has the power to dismiss the government. But ministers have to be formally sworn in by the president.