Scotland's largest jail can only house a further 160 prisoners before reaching crisis point, its governor has said.
HMP Barlinnie was designed to hold 1,018 prisoners
Bill McKinlay, governor at Barlinnie, was speaking as new figures revealed the prison housed 1,491 inmates.
The jail in Glasgow has a design capacity of 1,108 and Mr McKinlay said he did not want to go any higher.
Mr McKinlay said: "The numbers when I go into crisis are 1,665 and above. I would have to say to my director and my board, I can't take any more."
The governor said an increase in the prison population would impinge on the basic regime at Barlinnie.
"We would have to start closing down workshops and such like," he added.
The latest figures revealed the prison population on 22 February.