Error when Ec2 running as a role tries to get a Session Token in AWS

I'm running a app on an EC2 using a role with the the permissions:

"sts:GetSessionToken",
"sts:AssumeRole"

When I try to obtain temporary credentials using that role, I get the error:

Cannot call GetSessionToken with session credentials (Service: AWSSecurityTokenService; Status Code: 403; Error Code: AccessDenied;

Am I missing one or more permissions for the role to be able to obtain temporary session credentials?