Prison authorities are asking anyone who has booked a place on one of the public viewing days at Jurby but can't attend to get in touch.
Public tours of the new £41.7 million facility, which get under way this weekend, were oversubscribed within days of being advertised.
A number of people are on a reserve list and they will be invited to take the place of anybody who is unable to attend.
Those who are going are asked to turn up at least ten minutes early to allow time for security checks to be carried out, as tours must start promptly and groups cannot be held back for any latecomers.
Visitors are also reminded that items such as cameras and mobile phones cannot be taken inside the prison and should be locked up securely and out of sight.
(Picture: The view out of an open cell door at the new prison in Jurby).