According to the invention, in a hearing instrument it is once or repeatedly checked whether a second hearing instrument is present and active. If a second hearing instrument is active on the contralateral side, a first gain (corresponding to the gain for binaural fitting) is applied. If, however, no further hearing instrument is found to be active, a second—increased—gain is applied. The second gain may simply correspond to the first gain increased by a certain dB value. It may as an alternative be a specifically adapted gain characteristic of a monaural fitting for the user.