A seal (10) for a piezo-actuator of a fuel injector with terminal posts (12) projecting out of the piezo-actuator and a head arrangement (14) mounted on the piezo-actuator with openings (16) for passage of the terminal posts (12) is particularly suitable even for comparatively thin head plates. A sealing unit (18) mounted on the head arrangement (14) and provided with openings for passage of the terminal posts (12) is provided, having a support (22), on which a sealing material (26) is arranged, which is in contact in a sealing manner with the peripheral surfaces of the terminal posts (12) and a peripheral region of the head arrangement (14) and in which an element (20) made of microporous material is integrated to create gas permeability.