diff --git a/frontend/src/components/calendar/CalendarPage.tsx b/frontend/src/components/calendar/CalendarPage.tsx
index ba8899a..3f0543a 100644
--- a/frontend/src/components/calendar/CalendarPage.tsx
+++ b/frontend/src/components/calendar/CalendarPage.tsx
@@ -70,6 +70,14 @@ export default function CalendarPage() {
     return map;
   }, [calendars, sharedData]);
 
+  // Set of calendar IDs that are shared (owned or membership)
+  const sharedCalendarIds = useMemo(() => {
+    const ids = new Set<number>();
+    calendars.forEach((cal) => { if (cal.is_shared) ids.add(cal.id); });
+    sharedData.forEach((m) => ids.add(m.calendar_id));
+    return ids;
+  }, [calendars, sharedData]);
+
   // Handle navigation state from dashboard
   useEffect(() => {
     const state = location.state as { date?: string; view?: string; eventId?: number } | null;
@@ -158,7 +166,7 @@ export default function CalendarPage() {
   );
 
   const selectedEventPermission = selectedEvent ? permissionMap.get(selectedEvent.calendar_id) ?? null : null;
-  const selectedEventIsShared = selectedEvent ? permissionMap.has(selectedEvent.calendar_id) && permissionMap.get(selectedEvent.calendar_id) !== 'owner' : false;
+  const selectedEventIsShared = selectedEvent ? sharedCalendarIds.has(selectedEvent.calendar_id) : false;
 
   // Close panel if shared calendar was removed while viewing
   useEffect(() => {