procedure TJvDBGrid.CalcSizingState(X, Y: Integer; var State: TGridState;
  var Index: Longint; var SizingPos, SizingOfs: Integer;
  var FixedInfo: TGridDrawInfo);
var
	Coord: TGridCoord;
	DrawInfo: TGridDrawInfo; { My code }
begin
	inherited CalcSizingState(X, Y, State, Index, SizingPos, SizingOfs, FixedInfo);

	// do nothing if not authorized to size columns
	if not (dgColumnResize in Options) and not (csDesigning in ComponentState) then
		Exit;

	FCanResizeColumn := State = gsColSizing; //  If true, mouse double clicking can resize column.

(*
	// Mantis 5818: the inherited code sometimes gives an invalid index for the column
	if Index > LeftCol + VisibleColCount then
		Index := LeftCol + VisibleColCount;
*)

	{ Mantis 5818: fixed }
	{ My code }
	CalcDrawInfo(DrawInfo);
	if (DrawInfo.Horz.FullVisBoundary = DrawInfo.Horz.FixedBoundary) then begin
		Index := Index - 1;
	end;

	FResizeColumnIndex := Index - 1; // Store the column index to resize.

	if (State = gsNormal) and (Y <= RowHeights[0]) then
	begin
		Coord := MouseCoord(X, Y);
		CalcDrawInfo(FixedInfo);
		if CellRect(Coord.X, 0).Right - 5 < X then
		begin
			State := gsColSizing;
			Index := Coord.X;
			SizingPos := X;
			SizingOfs := X - CellRect(Coord.X, 0).Right;
		end;
		if CellRect(Coord.X, 0).Left + 5 > X then
		begin
			State := gsColSizing;
			Index := Coord.X - 1;
			SizingPos := X;
			SizingOfs := X - CellRect(Coord.X, 0).Left;
		end;
		if Index <= Byte(dgIndicator in Options) - 1 then
			State := gsNormal;
	end;
	FSizingIndex := Index;
	FSizingOfs := SizingOfs;
end;

procedure TJvDBGrid.CalcSizingState(X, Y: Integer; var State: TGridState;
  var Index: Longint; var SizingPos, SizingOfs: Integer;
  var FixedInfo: TGridDrawInfo);
var
	Coord: TGridCoord;
	DrawInfo: TGridDrawInfo;
begin
	inherited CalcSizingState(X, Y, State, Index, SizingPos, SizingOfs, FixedInfo);

	// do nothing if not authorized to size columns
	if not (dgColumnResize in Options) and not (csDesigning in ComponentState) then
		Exit;

	FCanResizeColumn := State = gsColSizing; //  If true, mouse double clicking can resize column.

	{ Mantis 5818: Index-out-of-range error when there is only one visible column partially displayed }
	CalcDrawInfo(DrawInfo);
	if (DrawInfo.Horz.FullVisBoundary = DrawInfo.Horz.FixedBoundary) then begin
		Index := Index - 1; // Index from inherited code has the value of 2.
	end;

	{ Store the column index to resize }
	if dgIndicator in Options then
		FResizeColumnIndex := Index - 1
	else
		FResizeColumnIndex := Index; // Mantis 6061

	if (State = gsNormal) and (Y <= RowHeights[0]) then
	begin
		Coord := MouseCoord(X, Y);
		CalcDrawInfo(FixedInfo);
		if CellRect(Coord.X, 0).Right - 5 < X then
		begin
			State := gsColSizing;
			Index := Coord.X;
			SizingPos := X;
			SizingOfs := X - CellRect(Coord.X, 0).Right;
		end;
		if CellRect(Coord.X, 0).Left + 5 > X then
		begin
			State := gsColSizing;
			Index := Coord.X - 1;
			SizingPos := X;
			SizingOfs := X - CellRect(Coord.X, 0).Left;
		end;
		if Index <= Byte(dgIndicator in Options) - 1 then
			State := gsNormal;
	end;
	FSizingIndex := Index;
	FSizingOfs := SizingOfs;
end;