Does CPF Hibernate Constraint not accept valid CPF?

I'm trying to run the Hibernate CPF validation constraint, but it just seems to reject valid CPF. The same test using the Email constraint normally works :

EmailValidator validator = new EmailValidator();
validator.isValid("[email protected]", null);

But the CPF, not:

CPFValidator cpfValidator = new CPFValidator();
cpfValidator.isValid("755.611.810-09", null);

What's the secret? I am using version 5.3.6. End of Hibernate Validator. I tried to remove the punctuation, but the result is the same: CPF is not valid.