diff --git a/polyfill/lib/calendar.mjs b/polyfill/lib/calendar.mjs
index 74cc9e1c6c..e70c811d0e 100644
--- a/polyfill/lib/calendar.mjs
+++ b/polyfill/lib/calendar.mjs
@@ -250,7 +250,7 @@ export class Calendar {
   }
   toJSON() {
     if (!ES.IsTemporalCalendar(this)) throw new TypeError('invalid receiver');
-    return ES.ToString(this);
+    return GetSlot(this, CALENDAR_ID);
   }
   static from(item) {
     const calendarSlotValue = ES.ToTemporalCalendarSlotValue(item);