diff --git a/packages/core/src/utils/plainDate.ts b/packages/core/src/utils/plainDate.ts
index a4d34d6a4d7..041dc3e6755 100644
--- a/packages/core/src/utils/plainDate.ts
+++ b/packages/core/src/utils/plainDate.ts
@@ -313,11 +313,8 @@ export const DATE_FORMAT_SHORT_WITH_YEAR: Intl.DateTimeFormatOptions = {
  *
  * The locale defaults to the same `'en'` fallback as `useLocale()`, avoiding
  * runtime-dependent output when no provider locale is available. Astryx date
- * APIs currently model Gregorian dates, so this helper defaults to Gregorian
- * when `options.calendar` is omitted. The explicit option remains supported for
- * compatibility with the public `Intl.DateTimeFormatOptions` signature; it is a
- * display-only escape hatch and does not change PlainDate arithmetic, parsing,
- * serialization, or any Astryx component's calendar semantics.
+ * APIs currently model Gregorian dates, so locale controls language and order
+ * but cannot select another calendar system.
  */
 export function plainDateFormat(
   pd: PlainDate,
@@ -326,7 +323,7 @@ export function plainDateFormat(
 ): string {
   return new Intl.DateTimeFormat(locale, {
     ...options,
-    calendar: options.calendar ?? 'gregory',
+    calendar: 'gregory',
   }).format(plainDateToDate(pd));
 }