diff --git a/dist/lib/core/wrapper/layout.d.ts b/dist/lib/core/wrapper/layout.d.ts
index 1115f3977..0e070a320 100644
--- a/dist/lib/core/wrapper/layout.d.ts
+++ b/dist/lib/core/wrapper/layout.d.ts
@@ -3,7 +3,7 @@ export declare class Layout extends Widget {
     static xtype: string;
     addItem(item: any): any;
     prependItem(item: any): any;
-    addItemAt(index: string, item: any): any;
+    addItemAt(index: number, item: any): any;
     removeItemAt(indexes: any): void;
     shouldUpdateItem(index: number, item: any): boolean;
     updateItemAt(index: number, item: any): any;
diff --git a/typescript/core/wrapper/layout.ts b/typescript/core/wrapper/layout.ts
index abc57bc55..48e4b3924 100644
--- a/typescript/core/wrapper/layout.ts
+++ b/typescript/core/wrapper/layout.ts
@@ -7,7 +7,7 @@ export declare class Layout extends Widget {
 
     prependItem(item: any): any;
 
-    addItemAt(index: string, item: any): any;
+    addItemAt(index: number, item: any): any;
 
     removeItemAt(indexes: any): void;