We propose a neutron diffraction study at HFM-EXED to determine the magnetic structures of two new high-field phases of LiNiPO4. In a recent pulsed-field experiment at SNS we identified the propagation vectors of these phases, which onset at 19T and 21T, respectively. One of the new phases was furthermore discovered to display a re-entrant magnetoelectric (ME) effect. Detailed knowledge of the magnetic structures in the two phases is paramount in order to arrive at a full understanding of the mechanism(s) responsible for magnetoelectricity in LiNiPO4. For the proposed experiment we kindly ask for 10 days of beamtime.