U.K. lawmakers voted to delay a decision on Boris Johnson’s Brexit deal, a move that will force the prime minister to ask the European Union to postpone Britain’s departure from the bloc.

Without sign-off from Parliament, Johnson is required by law to write to the EU by 11 p.m. tonight asking to delay Britain’s departure until Jan. 31.

On Saturday, lawmakers backed an amendment by former Tory minister Oliver Letwin and ex-Chancellor of the Exchequer Philip Hammond that withholds approval for the deal Johnson negotiated with the EU this week until the Withdrawal Agreement Bill that implements it becomes law.

Letwin and Hammond say their amendment is an insurance policy against Britain crashing out of the EU without an agreement by Johnson’s Oct. 31 deadline. The government may now put the Withdrawal Agreement Bill to lawmakers next week, paving the way for another crunch vote on Johnson’s Brexit plan before the month’s end.