For use in systems having multiple potential clock sources, circuitry and methods are used for selecting from among multiple clock sources and for preventing switching to an inactive clock source. Such clock switching circuitry and methods are used to detect an activity-status indication of the clock sources, generate a selection based update-enable signal responsive to the detected activity-status indication of the selected clock source, update a clock select input signal in response to a clock switch request for switching to the selected clock source and based on the generated selection based update-enable signal, and control switching to the selected clock source based on the updated clock select input signal.