U.S. District Judge Reed O’Connor has ruled that a 2022 regulation by the Biden administration targeting so-called “ghost guns” violates the Second Amendment and is unconstitutionally vague.

The measure, which required self-assembled firearms to be treated as if they had serial numbers, was struck down by the judge on two grounds. O’Connor determined it conflicts with the nation’s “historical tradition” of personal gunsmithing and self-manufacture, and also violates the Due Process Clause through its lack of clarity.

The regulation aimed to address ghost guns—firearms assembled from parts without serial numbers that allow owners to circumvent traditional firearm registration. However, data shows such firearms account for only approximately 1.5% of recovered guns at crime scenes in major U.S. cities.

Federal authorities reported receiving over 45,000 suspected ghost gun reports between 2016 and 2021, but confirmed instances were limited. In 2022 alone, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) processed more than 620,000 trace requests, with only about 19,000 identified as ghost guns.

The ruling follows a prior Supreme Court decision that upheld similar regulations but on narrower grounds. O’Connor’s decision marks the first time such a regulation has been invalidated on constitutional grounds in this manner.