A drunk man cut his head in a police station while two officers who arrested him were using their personal mobiles.
The man fell off a bench in Motherwell Police Station on 1 November and hurt the area above his left eye, according to the Police Investigations and Review Commissioner (Pirc).
He had earlier been arrested for being drunk and incapable.
The Pirc report found the injury may have been prevented had the officers not been distracted by their phones.
The 57-year-old, who hit his face against the bench and then the floor, had been assessed at hospital and was passed as fit to be detained.
He was taken back to hospital to be treated for the injury before being returned to the station. He was later released from custody and issued with a warning.
In the findings of its investigation, Pirc said the local police inspector took "prompt action" in providing advice and guidance to the officers, as well as issuing general guidance to staff in the command area about the importance of prisoner care.
Local police commander Ch Supt Alan Waddell said: "Our officers and staff work with commitment and professionalism day in, day out to provide a high quality policing service for the public, including those in our care.
"We accept the findings of the Pirc in relation to this incident.
"The local police inspector provided advice and guidance to the officers involved and issued general guidance to staff in his area about prisoner care."