It happened around 2 a.m. on eastbound I-40 near Reedy Creek Road.
The Highway Patrol says the driver of a car was preoccupied with his GPS when he slammed into the back of the deputy's car. The deputy was pulled over on the side of the road, assisting another motorist when it happened.
The deputy, whose name was not released, was taken to the hospital and is expected to be okay.
His patrol car, a Dodge Charger, was totaled in the crash.