The temperature dependence of the lattice parameters of CuSe up to 420 K showed that a phase transition from hexagonal to orthorhombic observed at about 398 K with decreasing temperature is second order and another transition from orthorhombic to hexagonal at 323 K is first order. The latter hexagonal phase has weak superlattice reflections in addition to main sublattice reflections. The intensities of weak superlattice reflections were increased by grinding the powder of CuSe at room temperature and they did not disappear over the temperature range of the orthorhombic phase only upon heating. These superlattice reflections pf this new but metastable phase can be indexed based on a monoclinic lattice.