diff --git a/sync_ics2gcal/gcal.py b/sync_ics2gcal/gcal.py
index e786e11..6c96cbd 100644
--- a/sync_ics2gcal/gcal.py
+++ b/sync_ics2gcal/gcal.py
@@ -86,7 +86,7 @@ class GoogleCalendar:
 
     logger = logging.getLogger('GoogleCalendar')
 
-    def __init__(self, service: discovery.Resource, calendarId: str):
+    def __init__(self, service: discovery.Resource, calendarId: Optional[str]):
         self.service: discovery.Resource = service
         self.calendarId: str = calendarId