The Arizona Supreme Court says police officers cannot frisk someone who’s armed unless they establish reasonable suspicion that criminal activity is occurring.

The court Thursday unanimously overturned the conviction of Johnathon Serna, who was searched by Phoenix police while out walking in October 2010. Police say an officer was speaking with Serna when he suspected Serna had a firearm. Serna confirmed he had a gun and the officer removed it from Serna’s waistband. When the officer asked a follow-up question, Serna admitted he had a prior felony conviction, which led to his arrest as a prohibited possessor of the firearm.

A Maricopa County Superior Court denied Serna’s motion that the search violated his Fourth Amendment rights and a jury convicted him of weapons misconduct. The state Court of Appeals upheld the conviction, but in their ruling the justices said there are “appropriate ways for officers to protect themselves once they learn a person is armed,” and that police need constitutional justification to search an individual.