diff --git a/angular-formly/angular-formly.d.ts b/angular-formly/angular-formly.d.ts
index 8c07ea800..f42b35a89 100644
--- a/angular-formly/angular-formly.d.ts
+++ b/angular-formly/angular-formly.d.ts
@@ -24,7 +24,7 @@ declare module AngularFormly {
 		data?: Object;
 		className?: string;
 		elementAttributes?: string;
-        fieldGroup: IFieldArray;
+        fieldGroup?: IFieldArray;
 		form?: Object;
 		hide?: boolean;
 		hideExpression?: string | IExpressionFunction;