The invention relates to a hose clamp for a blood treatment device, wherein the hose clamp has a housing (4) and an electromagnetically driven compression piece (1), with the electromagnetic drive of the compression piece (1) being configured such that the compression piece (1) is opened against a mechanical restoring force (A) in a state of the hose clamp with an applied current and is closed by the mechanical restoring force (A) in a currentless state of the hose clamp; wherein the hose clamp has, in addition to the electromechanical drive, a mechanical actuator (5) with which the compression piece (1) can be opened manually against the mechanical restoring force (A) in the currentless state of the hose clamp; and wherein the contact elements (6, 7) of the actuator (5) and of the compression piece (1) are configured such that they form a mechanical connection between the actuator (5) and the compression piece (1) after an opening of the compression piece (1) in the currentless state, said connection preventing another closing of the compression piece (1) in the currentless state of the hose clamp by the mechanical restoring force (A) and being released in the state of the hose clamp with an applied current.