Lincoln Park Zoo officials say they'll make changes to the walls of the new ape house after an invited group of human professional climbers were able to clamber out of the outdoor yard.
General Curator Robyn Barbiers said she's not happy with the result of the experiment, but she's happy to have exposed weaknesses now, before the animals move in.
The Regenstein Center for African Apes has been under construction at a cost of $25.7 million.
Barbiers said changes to the 12-foot-high walls will be made and the climbers will be invited back.
The building's resident chimpanzees and gorillas are scheduled to move into their new quarters in May.