Shares in budget airline Ryanair (LON:RYA) sunk on Monday after it issued another warning on Brexit, despite seeing profits for the quarter rise over 55 percent.

Profit after tax hit £397 million in the three months to June, with the airline making £11.40 profit on every passenger it carried during the period. Traffic rose 12 percent to 35 milliom as Ryanair’s lower fares and “Always Getting Better” led to a record 96 percent load factor.

Ryanair’s CEO Michael O’Leary commented on the stronger-than-expected figures:

“While Q1 average fares rose by 1 percent percent to just over £40, this was due to a strong April, boosted by Easter, offset by adverse sterling, lower bag revenue as more customers switch to our 2 free carry-on bag policy, and yield stimulation following a series of security events in Manchester and London.”

However, investor sentiment was dampened by a warning from O’Leary on the airline’s future in the wake of Brexit.

“We remain concerned at the uncertainty which surrounds the terms of the UK’s departure from the EU in March ’19. While we continue to campaign for the UK to remain in the EU Open Skies agreement, we caution that should the UK leave, there may not be sufficient time, or goodwill on both sides, to negotiate a timely replacement bilateral which could result in a disruption of flights between the UK and Europe for a period of time from April ’19 onwards”, he said.

“We, like all airlines, seek clarity on this issue before we publish our summer 2019 schedule in the second quarter of 2018. If we do not have certainty about the legal basis for the operation of flights between the UK and the EU by autumn 2018, we may be forced to cancel flights and move some, or all, of our UK based aircraft to Continental Europe from April ’19 onwards.”

The CEO’s warning led to Ryanair’s share price to fall on Monday, as investors take stock of the airline’s future. Shares are currently down 3.70 percent at 17.43 (1216GMT).