diff --git a/typescript/core/base.ts b/typescript/core/base.ts
index 40a216d76..e8793810c 100644
--- a/typescript/core/base.ts
+++ b/typescript/core/base.ts
@@ -263,7 +263,7 @@ export interface _base {
 
     isDeepMatch: (object: any, attrs: any) => boolean;
 
-    contains: (obj: any[], target: any, fromIndex?: number) => number;
+    contains: (obj: any[], target: any, fromIndex?: number) => boolean;
 
     deepContains: (obj: any[], copy: any) => number;