A device is described for longitudinally guiding a motor vehicle, including a sensor system for locating preceding vehicles, a controller that regulates the speed of the vehicle to a setpoint speed, either in a following driving mode as a function of the distance from a preceding vehicle or in a free driving mode, an interface to a navigation system which provides information about the traveled route, and a limiting device for limiting the setpoint speed based on the provided information. The limiting device is designed for calculating a limiting value for the setpoint speed for each possible route when the travel route is recognized as being ambiguous and for selecting the greatest of these limiting values for limiting the setpoint speed.