diff --git a/lcl/interfaces/win32/win32def.pp b/lcl/interfaces/win32/win32def.pp
index c6911e3f0b..6bf5017309 100644
--- a/lcl/interfaces/win32/win32def.pp
+++ b/lcl/interfaces/win32/win32def.pp
@@ -33,12 +33,6 @@ uses
   Windows, Classes, LCLType;
 
 const
-  // Used by TCalendar
-  MCM_FIRST = $1000;
-  MCM_GETCURSEL = MCM_FIRST + 1;
-  MCM_SETCURSEL =  MCM_FIRST + 2;
-  MCM_GETMINREQRECT = MCM_FIRST + 9;
-
   // it is not good to use WM_USER since many programs use it.
   WM_LCL_SOCK_ASYNC = WM_USER + $500;
 
@@ -56,4 +50,4 @@ var
 
 implementation
 
-end.
\ No newline at end of file
+end.
diff --git a/lcl/interfaces/win32/win32wscalendar.pp b/lcl/interfaces/win32/win32wscalendar.pp
index 3ded38a93d..485e6f0d87 100644
--- a/lcl/interfaces/win32/win32wscalendar.pp
+++ b/lcl/interfaces/win32/win32wscalendar.pp
@@ -33,9 +33,9 @@ uses
 // To get as little as posible circles,
 // uncomment only when needed for registration
 ////////////////////////////////////////////////////
-  Calendar, SysUtils, Controls, LCLType,
+  CommCtrl, SysUtils, Controls, LCLType, Calendar,
 ////////////////////////////////////////////////////
-  WSCalendar, WSLCLClasses, Windows, Win32Def, Win32WSControls;
+  WSCalendar, WSLCLClasses, WSProc, Windows, Win32WSControls;
 
 type
 
@@ -74,10 +74,12 @@ begin
     pClassName := 'SysMonthCal32';
     WindowTitle := StrCaption;
     Flags := WS_CHILD or WS_VISIBLE;
+    if dsShowWeekNumbers in TCustomCalendar(AWinControl).DisplaySettings then
+      Flags := Flags or MCS_WEEKNUMBERS;
     SubClassWndProc := @WindowProc;
   end;
   // create window
-  FinishCreateWindow(AWinControl, Params, false);
+  FinishCreateWindow(AWinControl, Params, False);
   Result := Params.Window;
   SetClassLong(Result, GCL_STYLE, GetClassLong(Result, GCL_STYLE) or CS_DBLCLKS);
   // resize to proper size
@@ -114,8 +116,17 @@ begin
 end;
 
 class procedure TWin32WSCustomCalendar.SetDisplaySettings(const ACalendar: TCustomCalendar; const ASettings: TDisplaySettings);
+var
+  Style: LongInt;
 begin
-  // TODO: implement me!
+  if not WSCheckHandleAllocated(ACalendar, 'TWin32WSCustomCalendar.SetDisplaySettings') then
+    Exit;
+  Style := GetWindowLong(ACalendar.Handle, GWL_STYLE);
+  if dsShowWeekNumbers in ASettings then
+    Style := Style or MCS_WEEKNUMBERS
+  else
+    Style := Style and not MCS_WEEKNUMBERS;
+  SetWindowLong(ACalendar.Handle, GWL_STYLE, Style);
 end;
 
 class procedure TWin32WSCustomCalendar.SetReadOnly(const ACalendar: TCustomCalendar; const AReadOnly: boolean);