  Equilibrium shape and orientation of vortex lattice are studied for an s-wave
tetrahedral superconductor in the vicinity of the upper critical field. The
phase diagram, which includes transitions between rhombic and rectangular
lattices, is constructed in the parameter space of the Ginzburg-Landau
functional. The developed theory is applied to the heavy-fermion superconductor
PrOs$_4$Sb$_{12}$. In a wide range of parameters the shape of the vortex
lattice is only weakly dependent on temperature. The neutron scattering
measurements of the vortex lattice in PrOs$_4$Sb$_{12}$ can be explained by a
peculiarities of the tetrahedral symmetry group and are further supported by
analysis of the appropriate band structure calculations.
