A fluid warmer (10) for temperature control of a medical fluid (14) guided in a fluid tube (12) and a method for operation thereof have a sensor (38), which determines a leakage current (40) via a functional grounding conductor (FE). Two supply connection conductors (22a; 22b) for a resistance heating element (18) as well as the functional grounding conductor (FE) are each equipped with a switch (30a; 30b; 30c) which can be controlled by a control device (32). The switches (30a; 30b; 30c) can be put into their open switching state jointly within a defined time interval by means of a control device (32) on occurrence of a leakage current (40) that is greater than or equal to a defined maximum threshold current magnitude (ITon, IToff).