A digital map enhancement system and a method performed by the system are disclosed for improving accuracy of pre-stored digital map data of a digital map to be utilized by a vehicle. The system determines a current position of the vehicle, and identifies, in the pre-stored digital map data, a mapped digital landmark representing a stationary landmark predicted to be in the vicinity of the current position of the vehicle, which mapped digital landmark includes a pre-stored position of the stationary landmark. The system detects the stationary landmark by one or more sensor devices on-board the vehicle, which are adapted for observing the surroundings of the vehicle, and determines a detected position of the stationary landmark based on the current position of the vehicle and the detection of the stationary landmark. The system updates the pre-stored position of the mapped digital landmark with the detected position of the stationary landmark.