An appeals court panel has ruled that a judge erred in dismissing the charges against Peterson more than a year ago.
Peterson was accused of having an assault rifle with a barrel shorter than 16 inches, which is illegal in Illinois. But a judge threw out the charge when Peterson's attorneys were not allowed access to certain prosecution documents.
The appeals court has decided that ruling was wrong.
Peterson is charged in the murder of his third wife, Kathleen Savio. He is also a suspect in the disappearance of his fourth wife, Stacy Peterson, but has not been charged with any wrongdoing in that case.
He has pleaded not guilty.
