ÁC 4 HO 4 À [systematic name: N,N-dibutylbenzenaminium 2-hydroxy-3,4-dioxocyclobut-1-en-1-olate], is composed of a protonated N,N-dibutylaniline cation with a hydrogen squarate monoanion (common names). The disparate bond lengths within the squarate anion suggest delocalization of the negative charge over only part of the squarate moiety. In the crystal, the squarate anions are linked by pairs of O-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (10) ring motif. The dimers are linked to the cations on either side by N-HÁ Á ÁO hydrogen bonds, and weak C-HÁ Á ÁO hydrogen bonds. These cation-anion-anion-cation units are linked by further C-HÁ Á ÁO hydrogen bonds, forming layers parallel to (102).