diff --git a/lcl/forms.pp b/lcl/forms.pp
index e0b21179e8..2a520ae074 100644
--- a/lcl/forms.pp
+++ b/lcl/forms.pp
@@ -137,6 +137,7 @@ type
     property Kind: TScrollBarKind read FKind;
     function GetOtherScrollBar: TControlScrollBar;
     property Size: integer read GetSize write SetSize stored False;
+    function ClientSize: integer; // return for vertical scrollbar the clientwidth
     function ClientSizeWithBar: integer; // return for vertical scrollbar the clientwidth with the bar, even if Visible=false
     function ClientSizeWithoutBar: integer; // return for vertical scrollbar the clientwidth without the bar, even if Visible=true
   published
diff --git a/lcl/include/buttons.inc b/lcl/include/buttons.inc
index d7b1699a67..15acb43af0 100644
--- a/lcl/include/buttons.inc
+++ b/lcl/include/buttons.inc
@@ -287,7 +287,7 @@ begin
     end;
   end;
   inherited WSSetText(AText);
-  //DebugLn(['TCustomButton.WSSetText ',dbgsName(Self),' Caption="',Caption,'" AutoSizeCanStart=',AutoSizeCanStart,' AutoSizeDelayed=',AutoSizeDelayed]);
+  //DebugLn(['TCustomButton.WSSetText ',dbgsName(Self),' Caption="',Caption,'"]);
 end;
 
 procedure TCustomButton.TextChanged;
diff --git a/lcl/include/controlscrollbar.inc b/lcl/include/controlscrollbar.inc
index 395f62c62e..9872f34e1f 100644
--- a/lcl/include/controlscrollbar.inc
+++ b/lcl/include/controlscrollbar.inc
@@ -490,22 +490,24 @@ begin
     Result := GetVertSCrollbar;
 end;
 
-function TControlScrollBar.ClientSizeWithBar: integer;
+function TControlScrollBar.ClientSize: integer;
 begin
   if Kind = sbVertical then
     Result:=FControl.ClientWidth
   else
     Result:=FControl.ClientHeight;
+end;
+
+function TControlScrollBar.ClientSizeWithBar: integer;
+begin
+  Result:=ClientSize;
   if not Visible then
     dec(Result,GetSize);
 end;
 
 function TControlScrollBar.ClientSizeWithoutBar: integer;
 begin
-  if Kind = sbVertical then
-    Result:=FControl.ClientWidth
-  else
-    Result:=FControl.ClientHeight;
+  Result:=ClientSize;
   if Visible then
     inc(Result,GetSize);
 end;
diff --git a/lcl/include/scrollingwincontrol.inc b/lcl/include/scrollingwincontrol.inc
index c0e1b5e19e..a700d6b599 100644
--- a/lcl/include/scrollingwincontrol.inc
+++ b/lcl/include/scrollingwincontrol.inc
@@ -121,14 +121,7 @@ function TScrollingWinControl.ComputeScrollbars: Boolean;
     OldAutoRange := p_Bar.FAutoRange;
     p_Bar.FAutoRange := 0;
     OtherScrollbar := p_Bar.GetOtherScrollBar;
-    if OtherScrollbar.FVisible then
-      SBSize := OtherScrollbar.Size
-    else
-      SBSize := 0;
-    if p_Bar.Kind = sbVertical then
-      SBSize := ClientHeight - SBSize
-    else
-      SBSize := ClientWidth - SBSize;
+    SBSize := OtherScrollbar.ClientSize;
     if (p_Bar.FRange > SBSize) and (SBSize > 0) then
       p_Bar.FAutoRange := (p_Bar.FRange - SBSize)
     else
@@ -145,14 +138,15 @@ var
   NewPage: Integer;
 begin
   Result := False;
-  // page
-  NewPage := Max(1,Min(ClientWidth - 1, High(HorzScrollbar.FPage)));
+
+  // page (must be smaller than Range and at least 1)
+  NewPage := Max(1,Min(VertScrollbar.ClientSize - 1, High(HorzScrollbar.FPage)));
   if NewPage <> HorzScrollbar.FPage then
   begin
     HorzScrollbar.FPage := NewPage;
     Result := True;
   end;
-  NewPage := Max(1,Min(ClientHeight - 1, High(VertScrollbar.FPage)));
+  NewPage := Max(1,Min(HorzScrollbar.ClientSize - 1, High(VertScrollbar.FPage)));
   if NewPage <> VertScrollbar.FPage then
   begin
     VertScrollbar.FPage := NewPage;
diff --git a/lcl/include/wincontrol.inc b/lcl/include/wincontrol.inc
index 116e57a377..7a913f4538 100644
--- a/lcl/include/wincontrol.inc
+++ b/lcl/include/wincontrol.inc
@@ -3292,7 +3292,7 @@ begin
   {$ENDIF}
   if not (caspComputingBounds in AutoSizePhases) then begin
     {$IFDEF VerboseAllAutoSize}
-    DebugLn(['TWinControl.DoAutoSize DELAYED AutoSizeCanStart=',AutoSizeCanStart,' AutoSizeDelayed=',AutoSizeDelayed,' AutoSizePhase=',AutoSizePhaseNames[AutoSizePhase]]);
+    DebugLn(['TWinControl.DoAutoSize DELAYED AutoSizePhase=',AutoSizePhaseNames[AutoSizePhase]]);
     {$ENDIF}
     Include(FControlFlags,cfAutoSizeNeeded);
     exit;