Theresa May says she has secured "legally binding" changes to her Brexit deal, a day ahead of MPs voting on it.
But European Commission President Jean-Claude Juncker warned if the deal was voted down there was "no third chance".
They spoke at a joint press conference in Strasbourg after a late meeting.
Labour leader Jeremy Corbyn said the prime minister's negotiations had "failed" and the announcements did not contain "anything approaching the changes" she had promised Parliament.
Cabinet Office Minister David Lidington announced the changes to the Commons shortly before the press conference, saying they would mean the EU "cannot try to trap the UK in the
Mrs May confirmed she would be opening the debate on Tuesday ahead of a so-called "meaningful vote" on her deal, which must be agreed by Parliament to come into force.
Last time her deal was put to Parliament in January, she suffered an historic loss as it was voted down by a margin of 230.
The PM also said her attorney general, Geoffrey Cox, would publish his legal advice on the changes to the deal before the vote.