A method for monitoring errors when testing a control program of a control device in a simulation environment, the control program being executed by an emulator on a computer, the emulator assigning an extended range of items to program variables of the control program, a variable value allocated to a program variable being stored in the extended range of items, the emulator marking program variables as erroneous or non-erroneous, the marking being carried out on the basis of an assignment of non-erroneous program variables to a first category and of erroneous program variables to a second category, or the marking being carried out on the basis of an error field stored in the extended range of items, a validity value being allocated to the error field of a non-erroneous program variable and an error value being allocated to the error field, of an erroneous program variable.