In the title compound, C(3)H(5)N(2)S(+)·H(2)PO(4) (-), the dihydrogen phosphate anions form infinite chains along [001] via short O-H⋯O hydrogen bonds. The 2-amino-thia-zolium cations inter-connect these chains into a three-dimensional network by short linear or bifurcated N-H⋯O and weak C-H⋯O hydrogen bonds.