diff --git a/src/irclib.py b/src/irclib.py
index 180979204..12a57a209 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -971,7 +971,7 @@ class IrcState(IrcCommandDispatcher, log.Firewalled):
         if prefix is None:
             prefix_chars = '@%+&~!'  # see the comments in addUser
         else:
-            prefix_chars = prefix.split(')', 1)[-1]
+            prefix_chars = ''.join(prefix.values())
 
         for item in items.split():
             stripped_item = item.lstrip(prefix_chars)
diff --git a/test/test_irclib.py b/test/test_irclib.py
index 18792e551..e747a2312 100644
--- a/test/test_irclib.py
+++ b/test/test_irclib.py
@@ -554,7 +554,8 @@ class IrcStateTestCase(SupyTestCase):
 
         # Prefixed with chars not in ISUPPORT PREFIX
         st = irclib.IrcState()
-        st.supported['PREFIX'] = '(ov)@+'
+        st.addMsg(self.irc, ircmsgs.IrcMsg(command='005',
+            args=('*', 'PREFIX=(ov)@+', 'are supported')))
         st.addMsg(self.irc, ircmsgs.IrcMsg(command='353',
             args=('*', '=', '#chan', 'nick1!u1@h1 @nick2!u2@h2 ~@nick3!u3@h3')))
         chan_st = st.channels['#chan']