diff --git a/highcharts/highstock.d.ts b/highcharts/highstock.d.ts
index 5f59e3694..f5133c54a 100644
--- a/highcharts/highstock.d.ts
+++ b/highcharts/highstock.d.ts
@@ -30,7 +30,7 @@ interface HighstockNavigatorOptions {
 
 interface RangeSelectorButton {
     type: string; //Defines the timespan, can be one of 'millisecond', 'second', 'minute', 'day', 'week', 'month', 'ytd' (year to date), 'year' and 'all'.
-    count: number;
+    count?: number;
     text: string;
     dataGrouping?: any; //not sure how this works
 }
@@ -117,4 +117,4 @@ interface JQuery {
     highcharts(type: string): HighchartsChartObject;
     highcharts(type: string, options: HighchartsOptions): JQuery;
     highcharts(type: string, options: HighchartsOptions, callback: (chart: HighchartsChartObject) => void): JQuery;
-}
\ No newline at end of file
+}