  It is known that non-holomorphic corrections are necessary in order to get
duality invariant free energy and entropy function. However the present methods
of incorporating non-holomorphic corrections are in conflict with special
geometry properties of moduli space. The moduli fields do not transform in
duality covariant way and their duality transformation also involves the
graviphoton field strength. In the present note we construct duality covariant
moduli fields for STU-model perturbatively in powers of the graviphoton field
strength and demonstrated their existence upto second order.
