diff --git a/lib/irc.js b/lib/irc.js
index 23ccfe08..2535e8b3 100644
--- a/lib/irc.js
+++ b/lib/irc.js
@@ -599,7 +599,7 @@ function Client(server, nick, opt) {
             case 'CAP':
                 if (message.args[0] === '*' &&
                      message.args[1] === 'ACK' &&
-                     message.args[2] === 'sasl ') // there's a space after sasl
+                     message.args[2].startsWith('sasl')) // there's a space after sasl
                     self.send('AUTHENTICATE', 'PLAIN');
                 break;
             case 'AUTHENTICATE':