diff --git a/src/irclib.py b/src/irclib.py
index 701dd1fb9..8396d5c86 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -821,6 +821,27 @@ class IrcState(IrcCommandDispatcher, log.Firewalled):
 
         return batches
 
+    def getClientTagDenied(self, tag):
+        """Returns whether the given tag is denied by the server, according
+        to its CLIENTTAGDENY policy.
+        This is only informative, and servers may still allow or deny tags
+        at their discretion.
+
+        For details, see the RPL_ISUPPORT section in
+        <https://ircv3.net/specs/extensions/message-tags>
+        """
+        tag = tag.lstrip("+")
+
+        denied_tags = self.supported.get('CLIENTTAGDENY')
+        if not denied_tags:
+            return False
+        denied_tags = denied_tags.split(',')
+        if '*' in denied_tags:
+            # All tags are denied by default, check the whitelist
+            return ('-' + tag) not in denied_tags
+        else:
+            return tag in denied_tags
+
     def do004(self, irc, msg):
         """Handles parsing the 004 reply
 
diff --git a/test/test_irclib.py b/test/test_irclib.py
index 0d870e93b..4342cdfa3 100644
--- a/test/test_irclib.py
+++ b/test/test_irclib.py
@@ -420,6 +420,29 @@ class IrcStateTestCase(SupyTestCase):
         self.assertEqual(state.supported['chanmodes'],
                          frozenset('biklmnopstveI'))
 
+    def testClientTagDenied(self):
+        state = irclib.IrcState()
+
+        # By default, every tag is assumed allowed
+        self.assertEqual(state.getClientTagDenied('foo'), False)
+        self.assertEqual(state.getClientTagDenied('bar'), False)
+
+        # Blacklist
+        state.addMsg(self.irc, ircmsgs.IrcMsg(
+            ':example.org 005 mybot CLIENTTAGDENY=foo :are supported by this server'))
+        self.assertEqual(state.getClientTagDenied('foo'), True)
+        self.assertEqual(state.getClientTagDenied('bar'), False)
+        self.assertEqual(state.getClientTagDenied('+foo'), True)
+        self.assertEqual(state.getClientTagDenied('+bar'), False)
+
+        # Whitelist
+        state.addMsg(self.irc, ircmsgs.IrcMsg(
+            ':example.org 005 mybot CLIENTTAGDENY=*,-foo :are supported by this server'))
+        self.assertEqual(state.getClientTagDenied('foo'), False)
+        self.assertEqual(state.getClientTagDenied('bar'), True)
+        self.assertEqual(state.getClientTagDenied('+foo'), False)
+        self.assertEqual(state.getClientTagDenied('+bar'), True)
+
     def testShort004(self):
         state = irclib.IrcState()
         state.addMsg(self.irc, ircmsgs.IrcMsg(':coulomb.oftc.net 004 testnick coulomb.oftc.net hybrid-7.2.2+oftc1.6.8'))