The invention relates to a method for adjusting a fuel/air ratio of an internal combustion engine (10), comprising a catalyst volume (26) with a first catalyst partial volume (26.1) and a second catalyst partial volume (26.2). The second catalyst partial volume (26.2) is arranged downstream from the first catalyst partial volume (26.1). An actual filling level of an exhaust gas constituent in the catalyst volume (26) is calculated from operating parameters of the internal combustion engine (10) and the exhaust system (14) using a computing model, and is adjusted to a nominal value by modifying the fuel/air ratio. The adjustment is carried out first for the second catalyst partial volume (26.2) and only later for the first catalyst partial volume (26.1).