diff --git a/src/channels.py b/src/channels.py
index c51f7da..f52f89c 100644
--- a/src/channels.py
+++ b/src/channels.py
@@ -4,6 +4,7 @@ from enum import Enum
 
 from src.context import IRCContext, Features, lower
 from src.events import Event
+from src import settings as var
 from src import users
 
 Main = None # main channel
@@ -259,6 +260,9 @@ class Channel(IRCContext):
                 if not self.modes[mode]:
                     del self.modes[mode]
         del user.channels[self]
+        if len(user.channels) == 0:
+            event = Event("cleanup_user", {})
+            event.dispatch(var, user)
 
     def _clear(self):
         for user in self.users:
diff --git a/src/users.py b/src/users.py
index 075a2b5..ca5e10c 100644
--- a/src/users.py
+++ b/src/users.py
@@ -1,16 +1,15 @@
-from weakref import WeakSet
 import fnmatch
 import re
 
 from src.context import IRCContext, Features, lower, equals
 from src import settings as var
-from src import db
+from src import db, events
 
 import botconfig
 
 Bot = None # bot instance
 
-_users = WeakSet()
+_users = set()
 
 _arg_msg = "(nick={0!r}, ident={1!r}, host={2!r}, realname={3!r}, account={4!r}, allow_bot={5})"
 
@@ -183,6 +182,14 @@ def parse_rawnick_as_dict(rawnick, *, default=None):
 
     return _raw_nick_pattern.search(rawnick).groupdict(default)
 
+def _cleanup_user(evt, var, user):
+    """Removes a user from our global tracking set once it has left all channels."""
+    _users.discard(user)
+
+# Can't use @event_listener decorator since src/decorators.py imports us
+# (meaning decorator isn't defined at the point in time we are run)
+events.add_listener("cleanup_user", _cleanup_user)
+
 class User(IRCContext):
 
     is_user = True