What are the requirements for AWS OpsWorks SSH keys?

Added an RSA deploy key to my private github repo, but when I add it to my OpsWorks rails app (paste public key into the "Repository SSH Key" field), and try to save, I get the error message "Please provide a valid SSH key".

Key was generated using ssh-keygen defaults (RSA 2048, no passphrase).

Not sure what else could be amiss.