diff --git a/lcl/interfaces/carbon/carbonproc.pp b/lcl/interfaces/carbon/carbonproc.pp
index ca1ffdf94e..6f64ddf98d 100644
--- a/lcl/interfaces/carbon/carbonproc.pp
+++ b/lcl/interfaces/carbon/carbonproc.pp
@@ -329,7 +329,7 @@ begin
   VK_SCROLL    : Result := MK_SCRLOCK;
   VK_SHIFT     : Result := MK_SHIFTKEY;
   VK_CONTROL   : Result := MK_COMMAND;
-  VK_MENU      : Result := MK_ALT;
+  VK_MENU      : Result := CarbonProc.MK_ALT; // see LCLType.MK_ALT
   VK_OEM_3     : Result := MK_TILDE;
 //VK_OEM_MINUS : Result := MK_MINUS;
   VK_OEM_PLUS  : Result := MK_EQUAL;
@@ -482,7 +482,7 @@ begin
   if (ButtonState and 4)         > 0 then Inc(Result, MK_MButton);
   if (shiftKey    and Modifiers) > 0 then Inc(Result, MK_Shift);
   if (controlKey  and Modifiers) > 0 then Inc(Result, MK_Control);
-  if (optionKey   and Modifiers) > 0 then Inc(Result, $20000000);
+  if (optionKey   and Modifiers) > 0 then Inc(Result, LCLType.MK_ALT); // see CarbonProc.MK_ALT
 
   //DebugLn('GetCarbonMsgKeyState Result=',dbgs(KeysToShiftState(Result)),' Modifiers=',hexstr(Modifiers,8),' ButtonState=',hexstr(ButtonState,8));
 end;
diff --git a/lcl/interfaces/cocoa/cocoautils.pas b/lcl/interfaces/cocoa/cocoautils.pas
index c8d1ecc1e1..acc949f799 100644
--- a/lcl/interfaces/cocoa/cocoautils.pas
+++ b/lcl/interfaces/cocoa/cocoautils.pas
@@ -846,7 +846,7 @@ begin
   VK_SCROLL    : Result := MK_SCRLOCK;
   VK_SHIFT     : Result := MK_SHIFTKEY;
   VK_CONTROL   : Result := MK_COMMAND;
-  VK_MENU      : Result := MK_ALT;
+  VK_MENU      : Result := CocoaUtils.MK_ALT; // LCLType.MK_ALT exists
   VK_OEM_3     : Result := MK_TILDE;
   VK_OEM_MINUS : Result := MK_MINUS;
   VK_OEM_PLUS  : Result := MK_EQUAL;
diff --git a/lcl/interfaces/cocoa/cocoawscommon.pas b/lcl/interfaces/cocoa/cocoawscommon.pas
index 5acbc308f7..4dc26a9f52 100644
--- a/lcl/interfaces/cocoa/cocoawscommon.pas
+++ b/lcl/interfaces/cocoa/cocoawscommon.pas
@@ -254,7 +254,7 @@ begin
   if AModifiers and NSControlKeyMask <> 0 then
     Result := Result or MK_CONTROL;
   if AModifiers and NSAlternateKeyMask <> 0 then
-    Result := Result or $20000000;
+    Result := Result or LCLType.MK_ALT; // see CocoaUtils.MK_ALT
 end;
 
 class function TLCLCommonCallback.CocoaPressedMouseButtonsToKeyState(AMouseButtons: NSUInteger): PtrInt;
@@ -490,7 +490,8 @@ var
     IsSysKey := (Event.modifierFlags and NSCommandKeyMask) <> 0;
     KeyData := (Ord(Event.isARepeat) + 1) or Event.keyCode shl 16;
     if (Event.modifierFlags and NSAlternateKeyMask) <> 0 then
-      KeyData := KeyData or $20000000;   // So that MsgKeyDataToShiftState recognizes Alt key, see bug 30129
+      KeyData := KeyData or LCLType.MK_ALT;   // So that MsgKeyDataToShiftState recognizes Alt key, see bug 30129
+                                              // see CocoaUtils.MK_ALT
     KeyCode := Event.keyCode;
 
     //non-printable keys (see mackeycodes.inc)
@@ -861,7 +862,8 @@ begin
   IsSysKey := (Event.modifierFlags and NSCommandKeyMask) <> 0;
   KeyData := (Ord(Event.isARepeat) + 1) or Event.keyCode shl 16;
   if (Event.modifierFlags and NSAlternateKeyMask) <> 0 then
-    KeyData := KeyData or $20000000;   // So that MsgKeyDataToShiftState recognizes Alt key, see bug 30129
+    KeyData := KeyData or LCLType.MK_ALT;   // So that MsgKeyDataToShiftState recognizes Alt key, see bug 30129
+                                            // see CocoaUtils.MK_ALT
   KeyCode := Event.keyCode;
 
   ignModChr := Event.charactersIgnoringModifiers;
diff --git a/lcl/interfaces/gtk3/gtk3widgets.pas b/lcl/interfaces/gtk3/gtk3widgets.pas
index 660fe10e6e..b4b40e6870 100644
--- a/lcl/interfaces/gtk3/gtk3widgets.pas
+++ b/lcl/interfaces/gtk3/gtk3widgets.pas
@@ -1494,7 +1494,7 @@ begin
     if AIsKeyEvent then
       Result := Result or KF_ALTDOWN
     else
-      Result := Result or $20000000;
+      Result := Result or MK_ALT;
   end;
 end;
 
@@ -1581,7 +1581,7 @@ begin
     ShiftState := ShiftState + [ssShift];
   if AState and MK_CONTROL <> 0 then
     ShiftState := ShiftState + [ssCtrl];
-  if AState and $20000000 <> 0 then
+  if AState and MK_ALT <> 0 then
     ShiftState := ShiftState + [ssAlt];
   // MappedXY := TranslateGdkPointToClientArea(AEvent^.scroll.window, EventXY,
   //                                        {%H-}TGtk3Widget(AWinControl.Handle).GetContainerWidget);
diff --git a/lcl/interfaces/mui/muibaseunit.pas b/lcl/interfaces/mui/muibaseunit.pas
index c346cce3ac..e81f78f78b 100644
--- a/lcl/interfaces/mui/muibaseunit.pas
+++ b/lcl/interfaces/mui/muibaseunit.pas
@@ -1574,9 +1574,9 @@ function KeyboardShiftState(State: Word): PtrInt;
 begin
   Result := 0;
   if State and IEQUALIFIER_LALT <> 0 then
-    Result := Result or $20000000;
+    Result := Result or MK_ALT;
   //if State and IEQUALIFIER_RALT <> 0 then
-  //  Result := Result or $20000000;
+  //  Result := Result or MK_ALT;
   //writeln('ShiftState AROS: ', HexStr(Pointer(State)), ' and ', HexStr(Pointer(IEQUALIFIER_LALT)),' -> ', HexStr(Pointer(Result)));
 end;
 
diff --git a/lcl/interfaces/qt/qtwidgets.pas b/lcl/interfaces/qt/qtwidgets.pas
index b0e97c0947..49c234e6f0 100644
--- a/lcl/interfaces/qt/qtwidgets.pas
+++ b/lcl/interfaces/qt/qtwidgets.pas
@@ -3820,7 +3820,7 @@ begin
     if AIsKeyEvent then
       Result := Result or KF_ALTDOWN
     else
-      Result := Result or $20000000;
+      Result := Result or MK_ALT;
   end;
     // $20000000;
   { TODO: add support for ALT, META and NUMKEYPAD }
@@ -3967,7 +3967,7 @@ begin
     Msg.State := [ssShift];
   if (ModifierState and MK_CONTROL) <> 0 then
     Msg.State := [ssCtrl] + Msg.State;
-  if (ModifierState and $20000000) <> 0 then
+  if (ModifierState and MK_ALT) <> 0 then
     Msg.State := [ssAlt] + Msg.State;
 
   LastMouse.WinControl := LCLObject;
diff --git a/lcl/interfaces/qt5/qtwidgets.pas b/lcl/interfaces/qt5/qtwidgets.pas
index 992f6542b3..fc53643c28 100644
--- a/lcl/interfaces/qt5/qtwidgets.pas
+++ b/lcl/interfaces/qt5/qtwidgets.pas
@@ -3747,7 +3747,7 @@ begin
     if AIsKeyEvent then
       Result := Result or KF_ALTDOWN
     else
-      Result := Result or $20000000;
+      Result := Result or MK_ALT;
   end;
     // $20000000;
   { TODO: add support for ALT, META and NUMKEYPAD }
@@ -3895,7 +3895,7 @@ begin
     Msg.State := [ssShift];
   if (ModifierState and MK_CONTROL) <> 0 then
     Msg.State := [ssCtrl] + Msg.State;
-  if (ModifierState and $20000000) <> 0 then
+  if (ModifierState and MK_ALT) <> 0 then
     Msg.State := [ssAlt] + Msg.State;
 
   LastMouse.WinControl := LCLObject;
diff --git a/lcl/lclintf.pas b/lcl/lclintf.pas
index 69642dd850..4e414e5c40 100644
--- a/lcl/lclintf.pas
+++ b/lcl/lclintf.pas
@@ -201,7 +201,7 @@ begin
   if GetKeyState(VK_SHIFT) < 0 then Include(Result, ssShift);
   if GetKeyState(VK_CONTROL) < 0 then Include(Result, ssCtrl);
   if GetKeyState(VK_LWIN) < 0 then Include(Result, ssMeta);
-  if KeyData and $20000000 <> 0 then Include(Result, ssAlt);
+  if KeyData and MK_ALT <> 0 then Include(Result, ssAlt);
 end;
 
 {$I winapi.inc}
diff --git a/lcl/lcltype.pp b/lcl/lcltype.pp
index 8601dec769..8859a53ff5 100644
--- a/lcl/lcltype.pp
+++ b/lcl/lcltype.pp
@@ -2835,6 +2835,7 @@ const
   MK_DOUBLECLICK = $80;
   MK_TRIPLECLICK = $100;
   MK_QUADCLICK = $200;
+  MK_ALT = $20000000;
 
 //==============================================
 // Constants from commctrl