An investigation has begun into how Gloucestershire Police responded to a call which was later linked to a sex attack on a 13-year-old girl.
The attack on the teenager, in School Lane, Quedgeley, was reported to officers on 16 October.
A 44-year-old man has been charged in connection with the incident.
The case has been referred to the Independent Police Complaints Commission after it emerged a call about an earlier assault was linked.
The IPCC said that during the criminal investigation, it became apparent that the call to the force from a member of the public concerning an assault in the same area was linked to the attack on the 13-year-old.
Gloucestershire Constabulary voluntarily referred the case to the IPCC, which will independently investigate the initial report and the police response to it.
IPCC Commissioner Rebecca Marsh said: "It is important that this case is independently examined to see how the original call from a concerned member of the public was handled and whether the police response was appropriate."
Assistant Chief Constable Kevin Lambert said: "We referred the case to the IPCC, who are carrying out an investigation into our call-handling and emergency response in this instance.
"We take our duty of care to members of our community very seriously, which is why we support the IPCC looking into whether we acted correctly as an organisation, in dealing with this very serious and distressing incident in its initial stages."
Colin Riddall, 44, of Redding Close in Quedgeley, is charged with kidnap, rape, false imprisonment, attempting to cause grievous bodily harm and possession of a knife in a public place, in connection with the attack on the 13-year-old.