diff --git a/src/conf.py b/src/conf.py
index 3b713f069..3c1df8e3e 100644
--- a/src/conf.py
+++ b/src/conf.py
@@ -339,10 +339,19 @@ class SpaceSeparatedSetOfChannels(registry.SpaceSeparatedListOf):
                 channels.append(channel)
             msg = ircmsgs.joins(channels_with_key + channels, keys)
             if len(str(msg)) > 512:
+                # Use previous short enough join message
                 msgs.append(old)
+                # Reset and construct a new join message using the current
+                # channel.
                 keys = []
                 channels_with_key = []
                 channels = []
+                if key:
+                    keys.append(key)
+                    channels_with_key.append(channel)
+                else:
+                    channels.append(channel)
+                msg = ircmsgs.joins(channels_with_key + channels, keys)
             old = msg
         if msg:
             msgs.append(msg)
diff --git a/test/test_conf.py b/test/test_conf.py
new file mode 100644
index 000000000..0fd50bc80
--- /dev/null
+++ b/test/test_conf.py
@@ -0,0 +1,59 @@
+##
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+#   * Redistributions of source code must retain the above copyright notice,
+#     this list of conditions, and the following disclaimer.
+#   * Redistributions in binary form must reproduce the above copyright notice,
+#     this list of conditions, and the following disclaimer in the
+#     documentation and/or other materials provided with the distribution.
+#   * Neither the name of the author of this software nor the name of
+#     contributors to this software may be used to endorse or promote products
+#     derived from this software without specific prior written consent.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+###
+
+from supybot.test import *
+
+import supybot.conf as conf
+import supybot.registry as registry
+import supybot.ircutils as ircutils
+
+
+class SupyConfTestCase(SupyTestCase):
+    def testJoinToOneChannel(self):
+        orig = conf.supybot.networks.test.channels()
+        channels = ircutils.IrcSet()
+        channels.add("#bar")
+        conf.supybot.networks.test.channels.setValue(channels)
+        msgs = conf.supybot.networks.test.channels.joins()
+        self.assertEqual(msgs[0].args, ("#bar",))
+        conf.supybot.networks.test.channels.setValue(orig)
+
+    def testJoinToManyChannels(self):
+        orig = conf.supybot.networks.test.channels()
+        channels = ircutils.IrcSet()
+        input_list = []
+        for x in range(1, 30):
+            name = "#verylongchannelname" + str(x)
+            channels.add(name)
+            input_list.append(name)
+        conf.supybot.networks.test.channels.setValue(channels)
+        msgs = conf.supybot.networks.test.channels.joins()
+        # Double check we split the messages
+        self.assertEqual(len(msgs), 2)
+        # Ensure all channel names are present
+        chan_list = (msgs[0].args[0] + ',' + msgs[1].args[0]).split(',')
+        self.assertCountEqual(input_list, chan_list)
+        conf.supybot.networks.test.channels.setValue(orig)