A seat track assembly may include a lower seat track having a pair of opposing outer rails and an upper seat track having a pair of opposing inner rails. The inner rails of the upper seat track may cooperate with the outer rails of the lower seat track to support the upper seat track for movement on the lower seat track. A support member may be provided between the lower seat track and the upper seat track. The support member may include a portion that extends in a vertical direction between the lower seat track and the upper seat track to restrict vertical movement of the upper seat track relative to the lower seat track. The support member may also include a portion that extends in a lateral direction between the inner rails of the upper seat track to restrict the inner rails from deforming inwardly toward one another.