Recent advances in X-ray free-electron lasers allow capturing of the diffraction pattern from a single nanoparticle before it disintegrates, in so-called ‘diffraction before destruction’ experiments. However, in order to reconstruct the nanoparticle structure from the diffraction pattern, the diffraction phase must be retrieved. Presently, the phase is reconstructed by iterative algorithms, imposing a non-convex computational challenge. Here we present a scheme for convex single-shot phase retrieval for two (or more) sufficiently separated objects, demonstrated in two dimensions (2D).