diff --git a/packages/svelte-ux/src/lib/utils/dateInternal.ts b/packages/svelte-ux/src/lib/utils/dateInternal.ts
index 4dafad8b1..6165ef57e 100644
--- a/packages/svelte-ux/src/lib/utils/dateInternal.ts
+++ b/packages/svelte-ux/src/lib/utils/dateInternal.ts
@@ -7,5 +7,5 @@ export function getWeekStartsOnFromIntl(locales?: string): DayOfWeek {
 
   const info = new Intl.Locale(locales);
   // @ts-ignore
-  return (info.weekInfo.firstDay ?? 0) % 7; // (in Intl, sunday is 7 not 0, so we need to mod 7)
+  return (info.weekInfo?.firstDay ?? 0) % 7; // (in Intl, sunday is 7 not 0, so we need to mod 7)
 }