Ryanair continued its worst-case scenario Brexit preparations this week, announcing that it will include a “Brexit clause” in flight bookings scheduled for summer 2019. Translation? Customers’ tickets may not be valid if the UK and EU don’t reach an alternative aviation deal before then.

Unlike other industries, which can rely on existing World Trade Organization rules after Brexit, the UK’s aviation industry has no fallback option when the Open Skies Agreement that currently allows EU airlines to fly freely within the bloc ceases to apply to Britain. The UK is scheduled to leave the EU in March 2019, and Ryanair is preparing for the event—hopefully avoidable—where flights between the UK and EU are grounded in absence of a deal.

The move comes after Ireland-based Ryanair applied to set up a UK subsidiary in December, which will allow it to operate its intra-UK routes as a domestic airline if a deal isn’t met. While industry watchers say it’s unlikely the EU and UK will fail to find an interim solution—both sides have a lot to lose—Ryanair is not taking any chances. The airline will release its summer 2019 schedule in September of this year and, for now, it has said customers will be refunded if their flights are cancelled under the so-called Brexit clause.

“We don’t see a regulatory solution yet,” said Ryanair marketing chief Kenny Jacobs. “If in the meantime between now and September, there’s a regulatory solution found, then those tickets will be sold as normal.”

Until then, sun-starved Brits will book their summer tickets with fingers firmly crossed./QUARTZ