A method for checking proper functioning of a fill-level measuring device working according to the travel time principle. For this purpose, in predetermined or selectable time intervals (ta), a current measured value curve at a current fill level (hactual) is ascertained; on the basis of the current measured value curve, a current wanted echo signal is determined. Subsequently, on the basis of the current wanted echo signal, an expected value (E) for quality of a wanted echo signal at least one predetermined fill level (hdesired) is ascertained. The ascertained expected value (E) for quality of the wanted echo signal at the predetermined fill level (hdesired) is compared with a predetermined critical value for quality, and an error condition is diagnosed, when the ascertained expected value falls below the critical value for quality.