diff --git a/components/tachart/tacustomseries.pas b/components/tachart/tacustomseries.pas
index 37d6031714..36234c41b5 100644
--- a/components/tachart/tacustomseries.pas
+++ b/components/tachart/tacustomseries.pas
@@ -1792,6 +1792,19 @@ begin
   if not Marks.IsMarkLabelsVisible or not Marks.AutoMargins then exit;
   if Count = 0 then exit;
 
+  {FLoBound and FUpBound fields may be outdated here (if axis' range has been
+   changed after the last series' painting). FLoBound and FUpBound will be fully
+   updated later, in a PrepareGraphPoints() call. But we need them now. If data
+   source is sorted, obtaining FLoBound and FUpBound is very fast (binary search) -
+   so we call FindExtentInterval() with True as the second parameter. If data
+   source is not sorted, obtaining FLoBound and FUpBound requires enumerating all
+   the data points to see, if they are in the current chart's viewport. But this
+   is exactly what we are going to do in the loop below, so obtaining true FLoBound
+   and FUpBound values makes no sense in this case - so we call FindExtentInterval()
+   with False as the second parameter, thus setting FLoBound to 0 and FUpBound to
+   Count-1}
+  FindExtentInterval(ParentChart.CurrentExtent, Source.IsSorted);
+
   for i := FLoBound to FUpBound do begin
     gp := GetGraphPoint(i);
     if not ParentChart.IsPointInViewPort(gp) then continue;
diff --git a/components/tachart/tagraph.pas b/components/tachart/tagraph.pas
index 016ccc8489..beb1cb1c37 100644
--- a/components/tachart/tagraph.pas
+++ b/components/tachart/tagraph.pas
@@ -322,7 +322,7 @@ type
     {$ENDIF}
     procedure Notification(
       AComponent: TComponent; AOperation: TOperation); override;
-    procedure PrepareAxis(ADrawer: IChartDrawer);
+      procedure PrepareAxis(ADrawer: IChartDrawer);
     function PrepareLegend(
       ADrawer: IChartDrawer; var AClipRect: TRect): TChartLegendDrawingData;
     procedure SetBiDiMode(AValue: TBiDiMode); override;
@@ -1465,10 +1465,12 @@ var
   prevExt: TDoubleRect;
   axis: TChartAxis;
   scDepth: Integer;
+  scSeriesMargins: TRect;
   scChartMargins: TRect;
   scMinDataSpace: Integer;
 begin
   scDepth := ADrawer.Scale(Depth);
+  scSeriesMargins := GetMargins(ADrawer);
   scChartMargins.Left := ADrawer.Scale(Margins.Left);
   scChartMargins.Right := ADrawer.Scale(Margins.Right);
   scChartMargins.Top := ADrawer.Scale(Margins.Top);
@@ -1478,7 +1480,7 @@ begin
   if not AxisVisible then begin
     FClipRect.Left += scDepth;
     FClipRect.Bottom -= scDepth;
-    CalculateTransformationCoeffs(GetMargins(ADrawer), scChartMargins, scMinDataSpace);
+    CalculateTransformationCoeffs(scSeriesMargins, scChartMargins, scMinDataSpace);
     exit;
   end;
 
@@ -1499,7 +1501,7 @@ begin
       SideByAlignment(FClipRect, aa, -axisMargin[aa]);
     prevExt := FCurrentExtent;
     FCurrentExtent := FLogicalExtent;
-    CalculateTransformationCoeffs(GetMargins(ADrawer), scChartMargins, scMinDataSpace);
+    CalculateTransformationCoeffs(scSeriesMargins, scChartMargins, scMinDataSpace);
     if prevExt = FCurrentExtent then break;
     prevExt := FCurrentExtent;
   end;