The crystal structure of the 1:1 proton-transfer compound of 8-aminoquinoline with toluene-4-sulfonic acid, viz. quinolin-8-aminium toluene-4-sulfonate, C9H9N2+烷H7O3S-, is different from previously characterized proton-transfer compounds of 8-aminoquinoline, in that the 8-amino group rather than the quinoline N atom is protonated. All H atoms of this aminium group are subsequently involved in intermolecular hydrogen-bonding interactions with sulfonate O-atom acceptors, linking the cationic and anionic species and forming a linear polymer structure.