One of the very controversial measures used by Ferguson police and St. Louis County police against people protesting the shooting of Michael Brown is their “5-second rule” —a crowd-control tactic that forces protesters to keep moving or be arrested if they remain in one place longer than 5 seconds.

Yesterday a federal judge issued a preliminary injunction against this tactic, because it violates the protesters’ constitutional rights.

The injunction “is a huge win for peaceful protesters and those who believe in the rule of law,” Tony Rothert, legal director of the ACLU, said in a news release.

Perry’s injunction said the practice police adopted, which some activists called the “five-second rule,” violated free speech rights. The judge also said the policy violated due process rights because “its enforcement was entirely arbitrary and left to the unfettered discretion of the officers on the street,” effectively making them lawmakers and enforcers.

“Citizens who wish to gather in the wake of Michael Brown’s tragic death have a constitutional right to do so, but they do not have the right to endanger lives of police officers or other citizens,” Perry wrote. “The police must be able to perform their jobs, and nothing in this order restricts their ability to do that.”