The crystal structure of the title compound (systematic name: 2-amino-1-methyl-4-oxo-4,5-dihydro-1H-imidazol-3-ium 3-phenylprop-2-enoate), C4H8N3O+·C9H7O2
−, is stabilized by N—H⋯O hydrogen bonding. Cations are linked to anions to form ion pairs with an R
2
2(8) ring motif. These ion pairs are connected through a C
2
2(6) chain motif extending along the c axis of the unit cell. This crystal packing is characterized by hydrophobic layers at x ∼ 1/2 packed between hydrophilic layers at x ∼ 0
