An arrangement for indicating correct installation of a plug-in unit (102) of a telecommunications device includes at least one distance indicator (106) located in the plug-in unit and adapted to produce an indication for correct installation of the plug-in unit in response to a situation where the distance of the distance indicator from a wall (107) of the frame of the telecommunications device is smaller than a predetermined threshold value. The distance indicator, which may be e.g. an electromechanical limit switch or capacitive distance sensor, is adapted to produce the indication for correct installation without a need for a galvanically conducted electric current between the distance indicator and the frame of the telecommunications device. There is thus no need to make any electric circuit arrangements in the frame of the telecommunications device for the indication of correct installation of a plug-in unit.