A robotic work tool system (200), comprising a robotic work tool (100), said robotic work tool (100) comprising a controller (110) being configured to cause said robotic work tool (100) to operate in a first operating mode, which first operating mode is based on a current position, said current position being determined based on signals received from a position determining device (190), such as Global Navigation Satellite System device (190); determine that said received signals are not reliable, and in response thereto cause said robotic work tool (100) to operate according to second operating mode, which second operating mode is not based on a current position being determined based on said received signals.