Any OT constraint banning a phonological entity in some position predicts that two types of languages should be attested: the ones which satisfy the constraint by changing the marked element and the ones where position of a marked element is modified. Yet for most such constraints, the languages which modify the marked element are attested but the ones modifying the position are not. The paper proposes a way to principally solve this problem within the framework of Serial OT. The solution consists in replacing the relevant OT constraints with constraints that specify position in the output of the previous derivational step (PS-constraints). Modifying position does not improve on PS-constraints since position in the output is irrelevant to their violation profile and position in the previous step cannot be changed by Gen. Adopting PS-constraints makes phonological theory more restrictive in a way that is compatible with the attested typology in the domain of voicing neutralization and syncope-stress interaction. The theory of PS-constraints is grounded in a precise definition of phonological position. If a constraint C mentions the elements of prosodic hierarchy both below and above the segmental level, the elements above the segmental level constitute position.