British Prime Minister Theresa May was dealt another humiliating blow Thursday as lawmakers voted against the latest incarnation of her Brexit plan.

While the vote was merely symbolic, parliament's refusal to back May's strategy for talks with the European Union represented another setback for the government as it attempts to renegotiate the terms of its Brexit deal with the EU.

Lawmakers voted 303 to 258 against a motion to endorse May's current approach to the talks, which include renegotiating the Irish backstop — a contentious part of the deal — along with a non-binding amendment to rule out a no-deal Brexit.

Both measures had previously been approved by parliament. But the inclusion of the latter amendment prompted hardline Brexiteers in May's Conservative party to abstain from Thursday's vote, as voting in favor of the motion would have implied that they approve of ruling out a scenario in which Britain crashes out of Europe on March 29 without a deal.

The defeat will further undermine May's pledge to the EU that if it renegotiates its deal with Britain, she can get a revised agreement approved by parliament.