A fitting for a sliding door, especially for furniture, comprises a rail (3) having at least one track (10, 11) on which one or more rollers (12) of a running part (6, 30) can move, and an anti-derailing mechanism (20, 40) which at least partly grips a section of the track (10, 11) of the rail (3) by means of a web (21, 41) that grips the anti-derailing mechanism (3) in the region of the at least one roller (12) when viewed in the longitudinal direction of the rail (3). This results in a compact anti-derailing mechanism.