A 19-year-old man presented on the Emergency Room on New Year's Eve with a 2 cm-wide black burn located on his lower arm. Earlier that evening he was hit by a piece of firework. Even though he immediately felt a sharp burning pain, he did not realize the severity of the injury. He presented with numbness in the digiti 4 and 5 and the Wartenberg sign, which are signs of an ulnar nerve injury. An exploration of the ulnar nerve was performed. Extensive burns and gunpowder were seen on the flexor carpi radialis and ulnaris muscle, the fascia and the epineurium of the ulnar nerve. However, the ulnar nerve was intact. A week later a babysitting procedure was performed because of absent intrinsic muscle activity, with an end-to-side anastomosis of the anterior interosseous nerve to the motor branch of the ulnar nerve. Hand physiotherapy was started after the operation.