diff --git a/src/views/components/calendar/utils.ts b/src/views/components/calendar/utils.ts
index 6cbe48ba..0a1ddc35 100644
--- a/src/views/components/calendar/utils.ts
+++ b/src/views/components/calendar/utils.ts
@@ -444,7 +444,8 @@ export const calculateCourseCellColumns = (dayCells: CalendarGridCourse[]) => {
                 typeof cell.calendarGridPoint.startIndex === 'number' &&
                 cell.calendarGridPoint.startIndex >= 0
         )
-        .toSorted((a, b) => a.calendarGridPoint.startIndex - b.calendarGridPoint.startIndex);
+        .slice()
+        .sort((a, b) => a.calendarGridPoint.startIndex - b.calendarGridPoint.startIndex);
 
     // Initialize metadata
     for (const cell of cells) {