The present disclosure relates to a fuel filter (1) for filtering diesel fuel supplied to an internal combustion engine (2). The fuel filter (1) includes a filter element (12, 19) for trapping and decomposing precipitates suspended in the diesel fuel. An solid acid catalyst Diesel out like a zeolite is provided for decomposing precipitates trapped by the filter element (12, 19). Sterol glycocides (precipitates) are splitted into sterol and glycosid moieties, which are soluble in the biodiesel, thus preventing clogging of the filter by sterol glycocide agglomerates. The sterol and glycosid moieties pass to the engine where they are burnt. The present disclosure also relates to a method of filtering diesel fuel for supply to an internal combustion engine (2).