A method and an engineering system, which reduce the extent of configuration work with regard to a possible expansion of the automation device. A configured automation device can thus be expanded during the control of the automation device by means of slave modules. During a configuration phase, the number of the slave units (11, 12, 13, 16, 17, 18) and a user data area for each slave unit can be configured. For each slave module of a slave unit, a portion of the user data area can be assigned. The user data area is prepared for a possible expansion of the slave unit by at least one slave module in that, in addition to the configured user data area of a respective slave unit required for the current control, a reserve user data area (11c, 11d, 13b, 13c, 13d, 16d, 18d) is configured for the at least one slave module.