def check_load_privatekey_callback_wrong_type(self):
        """
        Call the function with an encrypted PEM and a passphrase callback which
        returns a non-string.
        """
        for i in xrange(self.iterations * 10):
            try:
                load_privatekey(
                    FILETYPE_PEM, self.ENCRYPTED_PEM,
                    lambda *args: {})
            except ValueError:
                pass