Blocking of service in cellular radio system. An apparatus comprises a processor configured to control a stand-alone base station so that an emulated cell is formed by transmitting a control channel with information of a real cell and with such a transmission power that a subscriber terminal of a cellular radio system is forced to camp in the emulated cell, and to control the stand-alone base station to block service from the subscriber terminal before an integrity protection process is performed between the stand-alone base station and the subscriber terminal.