Emergency personnel responded to the scene, in the 400 block of 2nd Avenue North, at about 1:30 p.m. after receiving a report of a truck into a house.
A preliminary investigation found that the pickup was stopped nearby when the driver got out, thinking he had put the transmission in "park," said Leslie Hines of the Lynnwood Fire Department.
But after the driver left the pickup, it started rolling downhill with the driver's wife still inside.
The truck plowed through a fence and smashed into a storage shed, heavily damaging it.
The impact also broke off and pinched a gas line, causing a minor leak that was shut off by emergency personnel who responded to the scene.
No one was injured, but the shed was believed to be a total loss.