diff --git a/lcl/interfaces/carbon/carbonprivatewindow.inc b/lcl/interfaces/carbon/carbonprivatewindow.inc
index 223f6a9726..1d650fd588 100644
--- a/lcl/interfaces/carbon/carbonprivatewindow.inc
+++ b/lcl/interfaces/carbon/carbonprivatewindow.inc
@@ -116,6 +116,8 @@ const
   function GetMouseWheelDelta: Integer;
   var
     WheelDelta: SInt32;
+    CCtl: TCarbonCustomControl;
+    ScrollInfo: TScrollInfo;
   begin
     Result := 0;
     
@@ -127,7 +129,22 @@ const
     // Carbon's WheelDelta is the number of lines to be scrolled
     // LCL expects the delta to be 120 for each wheel step, which should scroll
     // Mouse.WheelScrollLines lines (defaults to three)
+    // Update: 20111212 by zeljko: All widgetsets sends WheelDelta +-120
+    // mac sends 1 or -1 so we just recalc that to wheel delta. see issue #20888
     Result := (120 * WheelDelta) div Mouse.WheelScrollLines;
+    if Widget.ClassType = TCarbonCustomControl then
+    begin
+      CCtl := TCarbonCustomControl(Widget);
+      if CCtl.GetScrollbarVisible(SB_VERT) then
+      begin
+        FillChar(ScrollInfo, SizeOf(ScrollInfo), #0);
+        ScrollInfo.fMask := SIF_TRACKPOS;
+        ScrollInfo.cbSize := SizeOf(ScrollInfo);
+        CCtl.GetScrollInfo(SB_VERT, ScrollInfo);
+        if (WheelDelta > 0) and (ScrollInfo.nTrackPos = 0) then
+          Result := 120;
+      end;
+    end;
     {$IFDEF VerboseMouse}
       DebugLn('GetMouseWheelDelta WheelDelta=', DbgS(WheelDelta), ' ', HexStr(WheelDelta, 8));
     {$ENDIF}
diff --git a/lcl/interfaces/qt/qtwidgets.pas b/lcl/interfaces/qt/qtwidgets.pas
index 8b27901216..fb9aef0c75 100644
--- a/lcl/interfaces/qt/qtwidgets.pas
+++ b/lcl/interfaces/qt/qtwidgets.pas
@@ -3277,6 +3277,9 @@ var
   MousePos: TQtPoint;
   Modifiers: QtKeyboardModifiers;
   ModifierState: PtrInt;
+  {$IFDEF DARWIN}
+  CCtl: TQtAbstractScrollArea;
+  {$ENDIF}
 begin
   Result := False;
   if not CanSendLCLMessage or (LCLObject = nil) then
@@ -3307,6 +3310,31 @@ begin
 
   Msg.WheelDelta := QWheelEvent_delta(QWheelEventH(Event));
 
+  {$IFDEF DARWIN}
+  // LCL expects delta +-120, we must fix it. issue #20888
+  if (ChildOfComplexWidget in [ccwCustomControl, ccwAbstractScrollArea,
+      ccwScrollingWinControl]) then
+  begin
+    if (Msg.WheelDelta > 0) then
+      Msg.WheelDelta := 1
+    else
+      Msg.WheelDelta := -1;
+    Msg.WheelDelta := (120 * Msg.WheelDelta) div Mouse.WheelScrollLines;
+    if FOwner <> nil then
+      CCtl := TQtAbstractScrollArea(FOwner)
+    else
+      CCtl := TQtAbstractScrollArea(Self);
+    //now fix ugly behaviour.
+    if (Msg.WheelDelta > 0) and (CCtl.FVScrollbar.getVisible) and
+        ((CCtl.FVScrollBar = Self) or
+         (Assigned(CCtl.FVScrollbar) and (Self <> CCtl.FHScrollbar))) then
+    begin
+      if CCtl.FVScrollbar.getSliderPosition <= 1 then
+        Msg.WheelDelta := 120;
+    end;
+  end;
+  {$ENDIF}
+
   NotifyApplicationUserInput(Msg.Msg);
   Result := DeliverMessage(Msg) <> 0;