diff --git a/history/ircplugin.py b/history/ircplugin.py
index 619103b..3fbb6bd 100644
--- a/history/ircplugin.py
+++ b/history/ircplugin.py
@@ -152,7 +152,7 @@ class History(Plugin):
     def _remove_channel_participant(self, where, who):
         """Remove the specified who from the where channel's participants list."""
         participants = self.channel_participants.setdefault(where, set())
-        participants.remove(who)
+        participants.discard(who)
         logger.debug("participants for %s: %s", where, participants)