diff --git a/src/gen-charts.ts b/src/gen-charts.ts
index efe0c95e..97644615 100644
--- a/src/gen-charts.ts
+++ b/src/gen-charts.ts
@@ -1574,7 +1574,7 @@ function makeChartType (chartType: CHART_NAME, data: IOptsChartData[], opts: ICh
strXml += ' '
strXml += ' '
strXml += ' '
- strXml += chartType === CHART_TYPE.PIE ? '' : ''
+ strXml += chartType === CHART_TYPE.PIE ? `` : ''
strXml += ' '
strXml += ' '
strXml += ' '