diff --git a/src/irclib.py b/src/irclib.py
index 5b7d93095..8b1898424 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -906,7 +906,8 @@ class Irc(IrcCommandDispatcher):
                 if not self.sasl_username:
                     log.error('SASL username is not set, unable to identify.')
                 else:
-                    auth_string = base64.b64encode('%s\x00%s\x00%s' % (self.sasl_username,
+                    auth_string =
+                    base64.b64encode('%s\x00%s\x00%s'.encode('utf-8') % (self.sasl_username,
                         self.sasl_username, self.sasl_password))
                     log.debug('Sending CAP REQ command, requesting capability \'sasl\'.')
                     self.queueMsg(ircmsgs.IrcMsg(command="CAP", args=('REQ', 'sasl')))