diff --git a/select2/select2.d.ts b/select2/select2.d.ts
index 259dd16cf..aa2c4a467 100644
--- a/select2/select2.d.ts
+++ b/select2/select2.d.ts
@@ -71,6 +71,7 @@ interface Select2Options {
     dropdownCss?: any;
     dropdownCssClass?: any;
     escapeMarkup?: (markup: string) => string;
+    theme?: string;
 }
 
 interface Select2JQueryEventObject extends JQueryEventObject {