In a first circuit for detecting clock glitches in a clock signal, a master counter is clocked by the clock signal and memorizes a master count. An incrementer advances the master count by one increment. A slave counter is clocked by the clock signal and memorizes a slave count. The slave count is retarded relative to the master count by at least a particular number of clock edges. A comparator determines whether the difference between the master count and the slave count is at least a value of the incrementer times the particular number of clock edges.