diff --git a/packages/hooks/src/useDatepicker/useDatepicker.ts b/packages/hooks/src/useDatepicker/useDatepicker.ts
index 8d1369a..3a86823 100644
--- a/packages/hooks/src/useDatepicker/useDatepicker.ts
+++ b/packages/hooks/src/useDatepicker/useDatepicker.ts
@@ -29,7 +29,7 @@ export interface OnDatesChangeProps {
   endDate: Date | null
 }
 
-export type FirstDayOfWeek = 0 | 1 | 2 | 3 | 4 | 5 | 6
+export type FirstDayOfWeek = 6 | 0 | 1 | 2 | 3 | 4 | 5
 
 export interface UseDatepickerProps {
   onDatesChange(data: OnDatesChangeProps): void
diff --git a/packages/hooks/src/useMonth/useMonth.utils.ts b/packages/hooks/src/useMonth/useMonth.utils.ts
index 87e5bb0..984c642 100644
--- a/packages/hooks/src/useMonth/useMonth.utils.ts
+++ b/packages/hooks/src/useMonth/useMonth.utils.ts
@@ -7,7 +7,7 @@ import getDay from 'date-fns/getDay'
 import startOfMonth from 'date-fns/startOfMonth'
 import startOfWeek from 'date-fns/startOfWeek'
 
-type FirstDayOfWeek = 0 | 1 | 2 | 3 | 4 | 5 | 6
+type FirstDayOfWeek = 6 | 0 | 1 | 2 | 3 | 4 | 5
 export interface GetWeekdayLabelsProps {
   firstDayOfWeek?: FirstDayOfWeek
   weekdayLabelFormat?(date: Date): string