diff --git a/resources/default_tweaks.py b/resources/default_tweaks.py
index beb8cbcb5b..c170f22ad2 100644
--- a/resources/default_tweaks.py
+++ b/resources/default_tweaks.py
@@ -575,3 +575,8 @@ allow_template_database_functions_in_composites = False
 # for https://whatever URLs. %u is replaced by the URL to be opened. The scheme
 # takes a glob pattern allowing a single entry to match multiple URL types.
 openers_by_scheme = {}
+
+#: Set the first day of the week for calendar popups
+# It must be one of the values Default, Sunday, Monday, Tuesday, Wednesday,
+# Thursday, Friday, or Saturday, all in English, spelled exactly as shown.
+calendar_start_day_of_week = 'Default'
diff --git a/src/calibre/gui2/widgets2.py b/src/calibre/gui2/widgets2.py
index 5e1e589fc7..6040479314 100644
--- a/src/calibre/gui2/widgets2.py
+++ b/src/calibre/gui2/widgets2.py
@@ -707,6 +707,12 @@ class DateTimeEdit(QDateTimeEdit):
         self.setMinimumDateTime(UNDEFINED_QDATETIME)
         self.setCalendarPopup(True)
         self.cw = CalendarWidget(self)
+        if tweaks['calendar_start_day_of_week'] != 'Default':
+            try:
+                dow = Qt.DayOfWeek[tweaks['calendar_start_day_of_week']]
+                self.cw.setFirstDayOfWeek(dow)
+            except Exception:
+                print(f"Bad value for tweak calendar_start_day_of_week: {tweaks['calendar_start_day_of_week']}")
         self.cw.setVerticalHeaderFormat(QCalendarWidget.VerticalHeaderFormat.NoVerticalHeader)
         self.setCalendarWidget(self.cw)
         self.setSpecialValueText(_('Undefined'))