In a hearing aid having a microphone to be arranged at a body of a user for capturing ambient sound, a loudspeaker for outputting the ambient sound after having been amplified on a frequency-dependent basis, and a signal processor, the signal processor is configured to amplify the sound such that the amplified sound is audible to the user, and to automatically re-adjust the gain by the following steps: selecting a tone having a specific frequency; outputting the tone and the amplified ambient sound via the loudspeaker as an output sound; capturing via said microphone an analysis sound composed of ambient sound and of a reflection of said output sound; extracting a reflection of the tone from the captured analysis sound; and determining a reflection component for the specific frequency of the tone; adjusting the gain in frequency-specific manner and based on the determined reflection component.