diff --git a/components/tachart/tacustomsource.pas b/components/tachart/tacustomsource.pas
index 982fcc5b7d..0c8c536101 100644
--- a/components/tachart/tacustomsource.pas
+++ b/components/tachart/tacustomsource.pas
@@ -94,6 +94,7 @@ type
     Text: String;
     YList: TDoubleDynArray;
     function GetY(AIndex: Integer): Double;
+    procedure SetY(AIndex: Integer; AValue: Double);
     procedure SetY(AValue: Double);
     procedure MultiplyY(ACoeff: Double);
     function Point: TDoublePoint; inline;
@@ -430,6 +431,14 @@ begin
     YList[i] := AValue;
 end;
 
+procedure TChartDataItem.SetY(AIndex: Integer; AValue: Double);
+begin
+  if AIndex = 0 then
+    Y := AValue
+  else
+    YList[AIndex - 1] := AValue;
+end;
+
 { TChartSourceBuffer }
 
 procedure TChartSourceBuffer.AddFirst(const AItem: TChartDataItem);