The US Supreme Court ruled that a huge chunk of Oklahoma, including much of Tulsa, falls within a Native American reservation.

The decision was a response to McGirt v. Oklahoma, in which Jimcy McGirt, a member of the Seminole Nation, was found guilty on the state level of a sex crime that happened within the Muscogee (Creek) Nation’s historical boundaries in 1997. McGirt argued that only federal authorities could prosecute him since state authorities have no power on Native American reservations.

The ruling overturned McGirt’s prison sentence though he could still be tried in federal court.

The Supreme Court ruling declares that Native Americans living on tribal lands can only be found guilty by federal prosecutors. This strips state courts of the power to prosecute Native Americans accused of crimes within tribal jurisdiction.

The Native American land in Oklahoma comprises three million acres, with a population of 1.8 million, 15 percent of which is Native American.

Supreme court Justices decided five-four for this ruling. Conservative Justice Neil Gorsuch sided with the court’s four liberal members on the matter, explaining that the United States must abide by the promise made in the 1830s that gave the Creek a permanent land in Oklahoma.