Code

import { DayPicker } from 'react-day-picker';
import { enAU } from 'date-fns/locale';
import * as dateFns from 'date-fns';

dateFns.setDefaultOptions({ locale: enAU });

export function App() {
  return <DayPicker dateLib={dateFns} mode='single' />;
}

Expected Behavior

I would expect the weekday column headers to correctly match up with the dates in the grid as pictured below:

Note: Friday 4th October 2024 is a correct date and appears in the two grids

locale explicitly set to enAU (locale={enAU}):

locale explicitly set to enUS (locale={enUS}):

Actual Behavior

When dateFns is supplied as the dateLib and has been setup with the default locale of enAU, the weekday headers render as enUS, but the grid renders as enAU, resulting in incorrect weekdays lining up with dates:

Note: Friday 5th October 2024 is not a correct date