diff --git a/packages/temporal-polyfill/src/internal/durationFields.ts b/packages/temporal-polyfill/src/internal/durationFields.ts
index 22dcce0b..fcbbac3a 100644
--- a/packages/temporal-polyfill/src/internal/durationFields.ts
+++ b/packages/temporal-polyfill/src/internal/durationFields.ts
@@ -52,7 +52,7 @@ export const durationFieldNamesAlpha = sortStrings(durationFieldNamesAsc)
 export const durationTimeFieldNamesAsc = durationFieldNamesAsc.slice(
   0,
   Unit.Day,
-)
+) as DurationTimeFieldName[]
 
 export const durationDateFieldNamesAsc = durationFieldNamesAsc.slice(Unit.Day)
 export const durationCalendarFieldNamesAsc = durationDateFieldNamesAsc.slice(1)