We present the low temperature gas-phase vibrational spectrum of ionised 1-cyanonaphthalene (1-CNN+) in the mid-infrared region. Experimentally, 1-CNN+ ions are cooled below 10 K in a cryogenic ion trapping apparatus, tagged with He atoms and probed with tuneable radiation. Quantum-chemical calculations are carried out at a density functional theory level. The spectrum is dominated by the CN-stretch at 4.516 μm, with weaker CH modes near 3.2 μm.