diff --git a/gateway/platforms/discord.py b/gateway/platforms/discord.py
index c05feb2ed..b94664dab 100644
--- a/gateway/platforms/discord.py
+++ b/gateway/platforms/discord.py
@@ -531,6 +531,11 @@ class DiscordAdapter(BasePlatformAdapter):
                 if message.author == self._client.user:
                     return
                 
+                # Ignore Discord system messages (thread renames, pins, member joins, etc.)
+                # Allow both default and reply types — replies have a distinct MessageType.
+                if message.type not in (discord.MessageType.default, discord.MessageType.reply):
+                    return
+                
                 # Bot message filtering (DISCORD_ALLOW_BOTS):
                 #   "none"     — ignore all other bots (default)
                 #   "mentions" — accept bot messages only when they @mention us
diff --git a/tests/gateway/test_discord_system_messages.py b/tests/gateway/test_discord_system_messages.py
new file mode 100644
index 000000000..8e2fb27e7
--- /dev/null
+++ b/tests/gateway/test_discord_system_messages.py
@@ -0,0 +1,99 @@
+"""Tests for Discord system message filtering (thread renames, pins, etc.)."""
+
+import pytest
+import unittest
+from unittest.mock import MagicMock
+
+discord = pytest.importorskip("discord")
+
+
+def _make_author(*, bot: bool = False, is_self: bool = False):
+    """Create a mock Discord author."""
+    author = MagicMock()
+    author.bot = bot
+    author.id = 99999 if is_self else 12345
+    author.name = "TestBot" if bot else "TestUser"
+    author.display_name = author.name
+    return author
+
+
+def _make_message(*, author=None, content="hello", msg_type=None):
+    """Create a mock Discord message with a specific type."""
+    msg = MagicMock()
+    msg.author = author or _make_author()
+    msg.content = content
+    msg.attachments = []
+    msg.mentions = []
+    msg.type = msg_type if msg_type is not None else discord.MessageType.default
+    msg.channel = MagicMock()
+    msg.channel.id = 222
+    msg.channel.name = "test-channel"
+    msg.channel.guild = MagicMock()
+    msg.channel.guild.name = "TestServer"
+    return msg
+
+
+class TestDiscordSystemMessageFilter(unittest.TestCase):
+    """Test that Discord system messages (thread renames, pins, etc.) are ignored."""
+
+    def _run_filter(self, message, client_user=None):
+        """Simulate the on_message filter logic and return whether message was accepted.
+
+        Replicates the guard added to discord.py:
+            if message.type not in (discord.MessageType.default, discord.MessageType.reply):
+                return  # ignored
+        """
+        # Own messages always ignored
+        if message.author == client_user:
+            return False
+
+        # System message filter (the fix being tested)
+        if message.type not in (discord.MessageType.default, discord.MessageType.reply):
+            return False
+
+        return True  # message accepted
+
+    def test_default_messages_accepted(self):
+        """Regular user messages (type=default) should be accepted."""
+        msg = _make_message(msg_type=discord.MessageType.default)
+        self.assertTrue(self._run_filter(msg))
+
+    def test_reply_messages_accepted(self):
+        """Reply messages (type=reply) should be accepted — users reply to bot messages."""
+        msg = _make_message(msg_type=discord.MessageType.reply)
+        self.assertTrue(self._run_filter(msg))
+
+    def test_thread_rename_ignored(self):
+        """Thread rename system messages should be ignored."""
+        msg = _make_message(msg_type=discord.MessageType.channel_name_change)
+        self.assertFalse(self._run_filter(msg))
+
+    def test_pins_add_ignored(self):
+        """Pin notifications should be ignored."""
+        msg = _make_message(msg_type=discord.MessageType.pins_add)
+        self.assertFalse(self._run_filter(msg))
+
+    def test_new_member_ignored(self):
+        """New member join messages should be ignored."""
+        msg = _make_message(msg_type=discord.MessageType.new_member)
+        self.assertFalse(self._run_filter(msg))
+
+    def test_premium_guild_subscription_ignored(self):
+        """Boost messages should be ignored."""
+        msg = _make_message(msg_type=discord.MessageType.premium_guild_subscription)
+        self.assertFalse(self._run_filter(msg))
+
+    def test_recipient_add_ignored(self):
+        """Group DM recipient add messages should be ignored."""
+        msg = _make_message(msg_type=discord.MessageType.recipient_add)
+        self.assertFalse(self._run_filter(msg))
+
+    def test_own_default_messages_still_ignored(self):
+        """Bot's own messages should still be ignored even if type is default."""
+        bot_user = _make_author(is_self=True)
+        msg = _make_message(author=bot_user, msg_type=discord.MessageType.default)
+        self.assertFalse(self._run_filter(msg, client_user=bot_user))
+
+
+if __name__ == "__main__":
+    unittest.main()