A misfire detection system for an internal combustion engine is disclosed with the system being used to evaluate wheel rpm fluctuations. This system detects a rough roadway over which the misfire detection is to be inhibited. This detection is made with the aid of wheel rpm signals; that is, signals as they are present for all motor vehicles equipped with anti-locking brake systems and for motor vehicles which utilize the wheel rpm signal for determining road speed. In motor vehicles of this kind, the advantage is provided that the wheel rpm signal has a double use. The advantage is provided that a reliable detection of a rough roadway is possible for all motor vehicles independently of whether wheel rpm signals are used for inhibiting the misfire detection or not.