diff --git a/src/components/common/CalendarModal.tsx b/src/components/common/CalendarModal.tsx
index ef5ce16f..7dbe6771 100644
--- a/src/components/common/CalendarModal.tsx
+++ b/src/components/common/CalendarModal.tsx
@@ -337,7 +337,7 @@ function buildCalendarGrid(year: number, month: number) {
   date.setDate(1);
   date.setMonth(month);
   date.setFullYear(year);
-  const firstDay = date.getDay();
+  const firstDay = date.getDay() || 7;
   const totalDaysInPrevMonth = new Date(year, month, 0).getDate();
 
   for (let i = 1; i < firstDay; i++) {