diff --git a/src/irclib.py b/src/irclib.py
index 4ccc5f1f2..551c08d02 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -157,7 +157,7 @@ class Channel(object):
 
     def addUser(self, user):
         nick = user.lstrip('@%+')
-        while user[0] in '@%+':
+        while user and user[0] in '@%+':
             (marker, user) = (user[0], user[1:])
             if marker == '@':
                 self.ops.add(nick)