diff --git a/plugins/Karma/config.py b/plugins/Karma/config.py
index 376348b20..fcc62db1f 100644
--- a/plugins/Karma/config.py
+++ b/plugins/Karma/config.py
@@ -66,5 +66,8 @@ conf.registerChannelValue(Karma, 'allowSelfRating',
 conf.registerChannelValue(Karma, 'allowUnaddressedKarma',
     registry.Boolean(True, _("""Determines whether the bot will
     increase/decrease karma without being addressed.""")))
+conf.registerChannelValue(Karma, 'onlyNicks',
+    registry.Boolean(False, _("""Determines whether the bot will
+    only increase/decrease karma for nicks in the current channel.""")))
 
 # vim:set shiftwidth=4 softtabstop=4 expandtab textwidth=79:
diff --git a/plugins/Karma/plugin.py b/plugins/Karma/plugin.py
index 2b8671530..c29bedabb 100644
--- a/plugins/Karma/plugin.py
+++ b/plugins/Karma/plugin.py
@@ -246,25 +246,34 @@ class Karma(callbacks.Plugin):
     def _doKarma(self, irc, msg, channel, thing):
         inc = self.registryValue('incrementChars', channel)
         dec = self.registryValue('decrementChars', channel)
-        if thing.endswith(tuple(inc + dec)):
-            for s in inc:
-                if thing.endswith(s):
-                    thing = thing[:-len(s)]
-                    if ircutils.strEqual(thing, msg.nick) and \
-                        not self.registryValue('allowSelfRating', channel):
+        onlynicks = self.registryValue('onlyNicks', channel)
+        karma = ''
+        for s in inc:
+            if thing.endswith(s):
+                thing = thing[:-len(s)]
+                # Don't reply if the target isn't a nick
+                if onlynicks and thing.lower() not in map(ircutils.toLower,
+                        irc.state.channels[channel].users):
+                    return
+                if ircutils.strEqual(thing, msg.nick) and \
+                    not self.registryValue('allowSelfRating', channel):
                         irc.error(_('You\'re not allowed to adjust your own karma.'))
                         return
-                    self.db.increment(channel, self._normalizeThing(thing))
-                    karma = self.db.get(channel, self._normalizeThing(thing))
-            for s in dec:
-                if thing.endswith(s):
-                    thing = thing[:-len(s)]
-                    if ircutils.strEqual(thing, msg.nick) and \
-                        not self.registryValue('allowSelfRating', channel):
-                        irc.error(_('You\'re not allowed to adjust your own karma.'))
-                        return
-                    self.db.decrement(channel, self._normalizeThing(thing))
-                    karma = self.db.get(channel, self._normalizeThing(thing))
+                self.db.increment(channel, self._normalizeThing(thing))
+                karma = self.db.get(channel, self._normalizeThing(thing))
+        for s in dec:
+            if thing.endswith(s):
+                thing = thing[:-len(s)]
+                if onlynicks and thing.lower() not in map(ircutils.toLower,
+                        irc.state.channels[channel].users):
+                    return
+                if ircutils.strEqual(thing, msg.nick) and \
+                    not self.registryValue('allowSelfRating', channel):
+                    irc.error(_('You\'re not allowed to adjust your own karma.'))
+                    return
+                self.db.decrement(channel, self._normalizeThing(thing))
+                karma = self.db.get(channel, self._normalizeThing(thing))
+        if karma:
             self._respond(irc, channel, thing, karma[0]-karma[1])
 
     def invalidCommand(self, irc, msg, tokens):
diff --git a/plugins/Karma/test.py b/plugins/Karma/test.py
index f615646d5..b5e4e5edc 100644
--- a/plugins/Karma/test.py
+++ b/plugins/Karma/test.py
@@ -204,4 +204,21 @@ class KarmaTestCase(ChannelPluginTestCase):
             karma.response.setValue(resp)
             karma.allowUnaddressedKarma.setValue(unaddressed)
 
+    def testOnlyNicks(self):
+        # We use this to join a dummy user to test upon
+        msg = ircmsgs.join(self.channel, prefix='hello!foo@bar')
+        self.irc.feedMsg(msg)
+        karma = conf.supybot.plugins.Karma
+        resp = karma.response()
+        onlynicks = karma.onlyNicks()
+        try:
+            karma.onlynicks.setValue(True)
+            karma.response.setValue(True)
+            self.assertSnarfNoResponse('abcd++')
+            self.assertSnarfRegexp('hello--', 'is now')
+            self.assertSnarfNoResponse('abcd--')
+            self.assertSnarfRegexp('hello++', 'is now')
+        finally:
+            karma.onlynicks.setValue(onlynicks)
+            karma.response.setValue(resp)
 # vim:set shiftwidth=4 softtabstop=4 expandtab textwidth=79: