Oklahoma Gov. Kevin Stitt signed a bill Tuesday explicitly prohibiting the use of nonbinary gender markers on state birth certificates, a ban experts say is the first of its kind in the nation.

The bill followed a flap last year over the Oklahoma State Department of Health’s agreement in a civil case allowing a nonbinary option. The birth certificate in that case was issued to an Oklahoma-born Oregon resident who sued after the agency initially refused the request. People who are nonbinary do not identify with traditional male or female gender assignments.