A method for operating parallel-connected inverter modules, wherein two or more inverter modules (A, B, C) are connected in parallel to feed the same load. Each inverter module has two or more output phases (u, v, w) for supplying electric power into a two or more phase load by determining the temperature (T_Au, T_Av, T_Aw, T_Bu, T_Bv, T_Bw, T_Cu, T_Cv, T_Cw) of each output phase (Au, Av, Aw, Bu, Bv, Bw, Cu, Cv, Cw) in each inverter module, comparing the temperatures of the output phases in each inverter module with the temperatures of the same output phase in other parallel-connected modules, and generating an alarm signal if the temperature of the output phase in an inverter module differs from the temperatures of the same output phase of the other inverter modules more than allowed by a predetermined limit.