diff --git a/chartjs/chart.d.ts b/chartjs/chart.d.ts
index a73ecc94e2..44d5718032 100644
--- a/chartjs/chart.d.ts
+++ b/chartjs/chart.d.ts
@@ -113,7 +113,7 @@ interface LinearInstance extends ChartInstance {
 interface CircularInstance extends ChartInstance {
     getSegmentsAtEvent: (event: Event) => {}[];
     update: () => void;
-    addData: (valuesArray: CircularChartData[], index: number) => void;
+    addData: (valuesArray: CircularChartData, index?: number) => void;
     removeData: (index: number) => void;
 }