2,3-Diamino-pyridinium hydrogen malonate

In the title mol-ecular salt, C5H8N3(+)·C3H3O4(-), the cation is essentially planar, with a maximum deviation of 0.005 (1) Å for all non-H atoms. In the anion, an intra-molecular O-H⋯O hydrogen bond generates an S(6) ring. In the crystal, the cations and anions are connected via N-H⋯O hydrogen bonds and a weak C-H⋯O inter-action, forming layers parallel to the ab plane.