diff --git a/jqueryui/jqueryui.d.ts b/jqueryui/jqueryui.d.ts
index a5df2c834..08058cca1 100644
--- a/jqueryui/jqueryui.d.ts
+++ b/jqueryui/jqueryui.d.ts
@@ -1704,7 +1704,7 @@ interface JQuery {
     sortable(methodName: string): JQuery;
     sortable(options: JQueryUI.SortableOptions): JQuery;
     sortable(optionLiteral: string, optionName: string): any;
-    sortable(methodName: 'serialize', options: { key?: string; attribute?: string; expression?: RegExp }): string;
+    sortable(methodName: 'serialize', options?: { key?: string; attribute?: string; expression?: RegExp }): string;
     sortable(optionLiteral: string, options: JQueryUI.SortableOptions): any;
     sortable(optionLiteral: string, optionName: string, optionValue: any): JQuery;