diff --git a/bot.py b/bot.py
index 40a0d95..fdea4cb 100644
--- a/bot.py
+++ b/bot.py
@@ -94,7 +94,7 @@ async def send_message(text):
 
 
 def get_event_id(event: Event) -> str:
-    return f"{event.begin}//{event.name}"
+    return f"{'_'.join(str(x) for x in event.begin.isocalendar())}//{event.name}"
 
 
 async def main():