diff --git a/include/wx/calctrl.h b/include/wx/calctrl.h
index de8881187e..02f50a14cd 100644
--- a/include/wx/calctrl.h
+++ b/include/wx/calctrl.h
@@ -27,7 +27,7 @@
 enum
 {
     // show Sunday as the first day of the week (default)
-    wxCAL_SUNDAY_FIRST               = 0x0000,
+    wxCAL_SUNDAY_FIRST               = 0x0080,
 
     // show Monday as the first day of the week
     wxCAL_MONDAY_FIRST               = 0x0001,
@@ -332,6 +332,9 @@ protected:
 
     // called by EnableHolidayDisplay()
     virtual void RefreshHolidays() { }
+
+    // does the week start on monday based on flags and OS settings?
+    bool WeekStartsOnMonday() const;
 };
 
 // ----------------------------------------------------------------------------
diff --git a/include/wx/generic/calctrlg.h b/include/wx/generic/calctrlg.h
index 0c2b48b413..0299b38a3c 100644
--- a/include/wx/generic/calctrlg.h
+++ b/include/wx/generic/calctrlg.h
@@ -202,13 +202,13 @@ private:
     // get the first/last days of the week corresponding to the current style
     wxDateTime::WeekDay GetWeekStart() const
     {
-        return HasFlag(wxCAL_MONDAY_FIRST) ? wxDateTime::Mon
+        return WeekStartsOnMonday() ? wxDateTime::Mon
                                            : wxDateTime::Sun;
     }
 
     wxDateTime::WeekDay GetWeekEnd() const
     {
-        return HasFlag(wxCAL_MONDAY_FIRST) ? wxDateTime::Sun
+        return WeekStartsOnMonday() ? wxDateTime::Sun
                                            : wxDateTime::Sat;
     }
 
diff --git a/interface/wx/calctrl.h b/interface/wx/calctrl.h
index 688c7fdf91..40bd51493d 100644
--- a/interface/wx/calctrl.h
+++ b/interface/wx/calctrl.h
@@ -8,7 +8,7 @@
 enum
 {
     // show Sunday as the first day of the week (default)
-    wxCAL_SUNDAY_FIRST               = 0x0000,
+    wxCAL_SUNDAY_FIRST               = 0x0080,
 
     // show Monday as the first day of the week
     wxCAL_MONDAY_FIRST               = 0x0001,
@@ -254,6 +254,11 @@ enum wxCalendarHitTestResult
     month is changed, so you will often want to update them in
     @c EVT_CALENDAR_PAGE_CHANGED event handler.
 
+    If neither the @c wxCAL_SUNDAY_FIRST or @c wxCAL_MONDAY_FIRST style is given,
+    the first day of the week is determined from operating system's settings,
+    if possible. The native wxGTK calendar chooses the first weekday based on
+    locale, and these styles have no effect on it.
+
     @beginStyleTable
     @style{wxCAL_SUNDAY_FIRST}
            Show Sunday as the first day in the week (not in wxGTK)
diff --git a/src/common/calctrlcmn.cpp b/src/common/calctrlcmn.cpp
index 5ab2542251..751b8b7458 100644
--- a/src/common/calctrlcmn.cpp
+++ b/src/common/calctrlcmn.cpp
@@ -195,5 +195,26 @@ bool wxCalendarCtrlBase::SetHolidayAttrs()
     return true;
 }
 
+bool wxCalendarCtrlBase::WeekStartsOnMonday() const
+{
+    if ( HasFlag(wxCAL_MONDAY_FIRST) )
+    {
+        return true;
+    }
+    else if ( HasFlag(wxCAL_SUNDAY_FIRST) )
+    {
+        return false;
+    }
+    else
+    {
+        // Neither flag was explicitly given, let's make a best guess
+        // based on locale and/or OS settings.
+
+        wxDateTime::WeekDay firstDay;
+        wxDateTime::GetFirstWeekDay(&firstDay);
+        return firstDay == wxDateTime::Mon;
+    }
+}
+
 #endif // wxUSE_CALENDARCTRL
 
diff --git a/src/generic/calctrlg.cpp b/src/generic/calctrlg.cpp
index d30e835f34..a3b396221f 100644
--- a/src/generic/calctrlg.cpp
+++ b/src/generic/calctrlg.cpp
@@ -245,6 +245,10 @@ void wxGenericCalendarCtrl::SetWindowStyleFlag(long style)
                     (m_windowStyle & wxCAL_SEQUENTIAL_MONTH_SELECTION),
                   wxT("wxCAL_SEQUENTIAL_MONTH_SELECTION can't be changed after creation") );
 
+    wxASSERT_MSG( !((style & wxCAL_SUNDAY_FIRST) &&
+                   (style & wxCAL_MONDAY_FIRST)),
+                 "wxCAL_SUNDAY_FIRST and wxCAL_MONDAY_FIRST cannot be both used" );
+
     wxControl::SetWindowStyleFlag(style);
 }
 
@@ -644,7 +648,7 @@ bool wxGenericCalendarCtrl::AdjustDateToRange(wxDateTime *date) const
 
 size_t wxGenericCalendarCtrl::GetWeek(const wxDateTime& date) const
 {
-    size_t retval = date.GetWeekOfMonth(HasFlag(wxCAL_MONDAY_FIRST)
+    size_t retval = date.GetWeekOfMonth(WeekStartsOnMonday()
                                    ? wxDateTime::Monday_First
                                    : wxDateTime::Sunday_First);
 
@@ -891,7 +895,7 @@ void wxGenericCalendarCtrl::OnPaint(wxPaintEvent& WXUNUSED(event))
         dc.SetPen(wxPen(m_colHeaderBg, 1, wxPENSTYLE_SOLID));
         dc.DrawRectangle(0, y, GetClientSize().x, m_heightRow);
 
-        bool startOnMonday = HasFlag(wxCAL_MONDAY_FIRST);
+        bool startOnMonday = WeekStartsOnMonday();
         for ( int wd = 0; wd < 7; wd++ )
         {
             size_t n;
@@ -1238,7 +1242,7 @@ bool wxGenericCalendarCtrl::GetDateCoord(const wxDateTime& date, int *day, int *
 
     if ( IsDateShown(date) )
     {
-        bool startOnMonday = HasFlag(wxCAL_MONDAY_FIRST);
+        bool startOnMonday = WeekStartsOnMonday();
 
         // Find day
         *day = date.GetWeekDay();
@@ -1479,7 +1483,7 @@ wxCalendarHitTestResult wxGenericCalendarCtrl::HitTest(const wxPoint& pos,
         {
             if ( wd )
             {
-                if ( HasFlag(wxCAL_MONDAY_FIRST) )
+                if ( WeekStartsOnMonday() )
                 {
                     wday = wday == 6 ? 0 : wday + 1;
                 }
diff --git a/src/msw/calctrl.cpp b/src/msw/calctrl.cpp
index 2567cc59d0..86b320bd02 100644
--- a/src/msw/calctrl.cpp
+++ b/src/msw/calctrl.cpp
@@ -152,11 +152,11 @@ WXDWORD wxCalendarCtrl::MSWGetStyle(long style, WXDWORD *exstyle) const
 
 void wxCalendarCtrl::SetWindowStyleFlag(long style)
 {
-    const bool hadMondayFirst = HasFlag(wxCAL_MONDAY_FIRST);
+    const bool hadMondayFirst = WeekStartsOnMonday();
 
     wxCalendarCtrlBase::SetWindowStyleFlag(style);
 
-    if ( HasFlag(wxCAL_MONDAY_FIRST) != hadMondayFirst )
+    if ( WeekStartsOnMonday() != hadMondayFirst )
         UpdateFirstDayOfWeek();
 }
 
@@ -427,7 +427,7 @@ void wxCalendarCtrl::UpdateMarks()
 void wxCalendarCtrl::UpdateFirstDayOfWeek()
 {
     MonthCal_SetFirstDayOfWeek(GetHwnd(),
-                               HasFlag(wxCAL_MONDAY_FIRST) ? MonthCal_Monday
+                               WeekStartsOnMonday() ? MonthCal_Monday
                                                            : MonthCal_Sunday);
 }
 
diff --git a/src/qt/calctrl.cpp b/src/qt/calctrl.cpp
index d2fbd8fcbd..c83474c179 100644
--- a/src/qt/calctrl.cpp
+++ b/src/qt/calctrl.cpp
@@ -107,9 +107,9 @@ void wxCalendarCtrl::UpdateStyle()
     if ( !m_qtCalendar )
         return;
 
-    if ( m_windowStyle & wxCAL_MONDAY_FIRST )
+    if ( WeekStartsOnMOnday() )
         m_qtCalendar->setFirstDayOfWeek(Qt::Monday);
-    else // wxCAL_SUNDAY_FIRST
+    else
         m_qtCalendar->setFirstDayOfWeek(Qt::Sunday);
 
     if ( m_windowStyle & wxCAL_SHOW_WEEK_NUMBERS )