A newly designated “military installation” that stretches the length of the frontier in New Mexico has made trespassing a novel criminal charge at the border, bringing turmoil to the state. A judge says migrants couldn’t know they were trespassing.

A U.S. judge in New Mexico on Thursday dismissed trespassing charges against dozens of migrants caught in a new military zone on the U.S.-Mexico border, marking a setback for Trump administration efforts to raise penalties for illegal crossings.