The present disclosure relates to membranes for use in electrolysis systems. The teachings thereof may be embodied in a method for checking a membrane of an electrolyzer comprises two volumes separated by the membrane and produces two product gases from a starting liquid. The method may include: detecting an electrolysis current strength during electrolysis, measuring a liquid flow rate of the starting liquid between the two electrolyzer volumes, calculating a ratio of the measured liquid flow rate and the detected electrolysis current strength, and using the calculated ratio as an indication of membrane leaktightness.