Sex offenders held at a Norfolk prison were not adequately prepared for resettlement, according to inspectors.
HMP Bure was "safe" but needed to improve its management of the risks these inmates posed, they found.
The prison, built on the former RAF Coltishall, houses 650 inmates and is "national resource for sex offenders", chief inspector Peter Clarke said.
Work to address weaknesses in resettlement support was taking place, the prison service said.
Inspectors were pleased to find the prison was "safe" with low levels of violence.
Living conditions were decent, staff-prisoner relationships were generally good and there was sufficient work, training and education for all, the HM Inspectorate of Prisons report said, following an unannounced inspection in March and April.
Few prisoners self-harmed but support for those with complex and ongoing needs was weak.
"But as a national resource for sex offenders, the prison had no resettlement function and very limited resources to support reintegration and resettlement back in to the community," the report highlighted.
Mr Clarke said: "Bure was a safe and decent prison, but weaknesses in offender management and resettlement - requirements which should be at the very heart of the prison's purpose - undermined its success and overall effectiveness."
Michael Spurr, chief executive of HM Prison and Probation Service, said."The governor and her staff at HMP Bure deserve credit for providing a positive regime for prisoners in a safe and respectful environment.
"Work is already under way to address the weaknesses identified in offender management and resettlement support and the governor is using the recommendations in this report to drive progress in these areas."