A seat length adjuster for a vehicle seat may have two rail pairs, each pair formed by an upper rail and a lower rail. The upper rail is provided with openings and the lower rail has through holes. At least one spring-loaded, movable locking member may be provided. The locking member carries toothlike protrusions on its two opposite lengthwise sides, which are movable from a released position into the locked position both into the openings and into the through holes. The openings and/or the through holes have contact regions for the toothlike protrusions of the locking member and at least some of the toothlike protrusions have a respective undercut on both tooth flanks. In the locked position a projecting edge resulting from this on the respective tooth flank lies opposite the contact region and/or touches this contact region.