United Airlines will now offer travelers booking flights nonbinary gender options for identifying themselves, the airline announced Friday.

"United is determined to lead the industry in LGBT inclusivity, and we are so proud to be the first U.S. airline to offer these inclusive booking options for our customers," said United's Chief Customer Officer Toby Enqvist in a statement.

Fly how you identify. Our new non-binary gender options are now available. — United Airlines (@united) March 22, 2019

"Welcome Aboard, Mx.," the statement proclaimed.

United flyers can now identify as M(male), F(female), U(undisclosed) or X(unspecified), and will have the option to choose the title "Mx" while booking a flight.

The airline's statement said it worked with LGBT groups, Human Rights Campaign and the Trevor Project, to train employees about preferred pronouns and "the persistence of gender norms."

"By providing non-binary gender selection for ticketing and the gender-inclusive honorific 'Mx' in user profiles, United Airlines is taking an important step forward for non-binary inclusion," said Beck Bailey, acting director of Human Rights Campaign's Workplace Equality Program.