A filter system for filtering fluids has a housing, an inlet, and an outlet. A filter element is arranged inside the housing. A cover closes the housing and provides access to the filter element inside the housing. A securing device prevents the housing from being closed by the cover when the filter element is missing. The filter element has at least one filter element guide path section. The housing or the cover has a rim area with at least one rim guide path section. The filter element guide path section and the rim guide path section supplement one another to a guide path. The securing device comprises at least one securing element arranged on the cover or the housing. The securing element is guided on the guide path when a closing movement is carried out for closing the housing by the cover.