She might be 7,000 miles away, but Theresa May's colleagues at home - including those she promoted - have the capacity to ruin her night.
Just as she was sitting down to at a glittering evening with her fellow world leaders, news broke that Sam Gyimah had just become the latest minister to quit over Brexit.
He had a specific reason to leave. As a science minister, he was frustrated with arguments between the UK and the EU over the satellite programme Galileo.
It's only today that the prime minister confirmed that the UK was giving up on those talks.
But it is his overall verdict on Mrs May's Brexit compromise that will really hurt.
Mr Gymiah was a Remainer, but an early backer of the prime minister and part of her leadership campaign back in 2018.
However, his words are strong - this is not just a minor grump.
He slams her agreement with the EU overall, judging that it is not in the national interest and sets up the country for failure, leaving us poorer, weaker, and less secure.
He even says the idea of another referendum should not be dismissed, even if that means the legal process of departure, Article 50, has to be extended.
There is some comfort overnight for Mrs May from Michael Gove, who as one of the leading voices in the Leave campaign is, belatedly perhaps, urging his Brexiteer colleagues to get onboard.
In an article for the Daily Mail, Mr Gove warns that if they vote down the PM's compromise, Brexit itself is under threat.
But this latest resignation is another sign of how hard it will be for the prime minister to pass the vote that could define her future.
And perhaps while Brexiteer anger about the deal has been raging for weeks, more former Remainers are yet to voice their fears.
One former minister suggested that ministers with doubts, of which there are many, may now be deciding to call time, saying, "they are not prepared to go over the cliff for a rotten deal that will be voted down anyway".
It's not certain that will happen. But Mr Gyimah is one fewer vote for Mrs May's compromise deal, when she desperately needs every single one.