Montana’s Supreme Court has upheld a landmark climate ruling that said the state was violating residents’ constitutional right to a clean environment.

The 6-1 ruling is a major, and rare, victory for climate activists, who have tried to use the courts to force action on government and corporate policies and activities they say are harming the planet.

The Montana Supreme Court on Wednesday upheld a district court ruling in the nation’s first constitutional climate change trial, affirming that the youth plaintiffs have a “fundamental constitutional right to a clean and healthful environment” while revoking two Montana statutes.