A report says there are too few staff at Woodhill Prison in Milton Keynes.
Prison governor says staff numbers will increase
The study, by Her Majesty's Inspector of Prisons, comes a year after an inspection at Woodhill last February.
It highlights two major concerns, both linked to low staff numbers.
The report also says suicide monitoring at the jail needs to be improved.
But the report did praise the staff for maintaining a positive attitude.
Woodhill's governor Bob Mullen said they were working to address the staffing problem and had just taken on 46 new employees.