diff --git a/app/[locale]/calendar/page.tsx b/app/[locale]/calendar/page.tsx
index 398abaa2..310b6dc1 100644
--- a/app/[locale]/calendar/page.tsx
+++ b/app/[locale]/calendar/page.tsx
@@ -615,7 +615,7 @@ export default function CalendarPage() {
 
   const visibleEvents = useMemo(() =>
     events.filter((e) => {
-      if (!e.calendarIds) return false;
+      if (!e.start || !e.calendarIds) return false;
       const calIds = Object.keys(e.calendarIds);
       return calIds.some((id) => selectedCalendarIds.includes(id));
     }),
diff --git a/stores/calendar-store.ts b/stores/calendar-store.ts
index 17f71f10..44f9b94b 100644
--- a/stores/calendar-store.ts
+++ b/stores/calendar-store.ts
@@ -110,10 +110,12 @@ export const useCalendarStore = create<CalendarStore>()(
       fetchEvents: async (client, start, end) => {
         set({ isLoadingEvents: true, error: null });
         try {
-          const events = await client.queryAllCalendarEvents({
+          const rawEvents = await client.queryAllCalendarEvents({
             after: start,
             before: end,
           });
+          // Filter out malformed events missing required 'start' field
+          const events = rawEvents.filter(e => typeof e.start === 'string' && e.start);
           set({ events, isLoadingEvents: false, dateRange: { start, end } });
         } catch (error) {
           debug.error('Failed to fetch events:', error);