This proposal is part of our research programme to investigate quantum magnets on frustrated lattices in search for novel types of magnetic order and spin dynamics. Here we propose to determine the magnetic order in the spin-1/2 square lattice antiferromagnet PbVO3. Structural studies and band-structure calculations proposed that it may be a unique realization of a square lattice with strong diagonal bond frustration that would strongly suppress the tendency to magnetic order. Indeed temperature-dependent susceptibility and specific heat data observe no clear anomalies at low temperatures suggesting that if long-range magnetic order occurs the moments would be rather small. Here we propose to use the highly-sensitive diffraction bank on Osiris to search for magnetic order with small moments and/or diffuse scattering indicative of short-range order and also look for a possible spin gap.