A thirteen-year-old boy accidentally shot his nine-year-old sister with a hunting rifle at their Hillsboro home, police said.

The boy was cleaning the rifle as the family prepared for a camping trip and he accidentally discharged it, police said. The bullet went through the wall and hit his young sister in the shoulder.

The children’s mother immediately called 9-1-1 and the girl was rushed to Oregon Health and Science University, where she was treated and released.

Detectives said the shooting was ruled accidental and was a prime example of why locks should be used on guns kept inside homes.

“Teaching children gun safety is critical for people who have guns in their households,” Sgt. Vance Stimler with the Washington County Sheriff’s Office said.

The Washington County Sheriff’s Office gives away free locks at their main office or local precincts.