Clasp for a watch bracelet or for a garment belt comprising at least two unfolding arms articulated to each other; a first unfolding arm comprises a first end attached to a bracelet strand and a second end pivotally articulated to a first end of a second unfolding arm; a second end of the second unfolding arm is traversed by an arbour about which there is articulated a cover provided with first and second flaps and to which another bracelet strand is attached; the clasp also comprises a push button fastening system, characterized in that at least one push button controls a bolt pivotally mounted on the cover; the bolt comprises a first hook devised to cooperate with a second hook fitted to the first unfolding arm and to keep said second hook locked when the push button is not being manually activated, the first hook being kept engaged with the second hook by an elastic means.