diff --git a/typescript/core/base.ts b/typescript/core/base.ts
index b5a3ce55c..6182a0833 100644
--- a/typescript/core/base.ts
+++ b/typescript/core/base.ts
@@ -148,9 +148,9 @@ export interface _base {
 
     takeRight: <T>(array: T[], n: number) => T[];
 
-    findIndex: (array: any[], value: any, callback?: Function | object | string, thisArg?: any) => number;
+    findIndex: <T>(array: T[], predicate?: ((index: number, item: T, array: T[]) => any) | object | string, thisArg?: any) => number;
 
-    findLastIndex: (array: any[], value: any, callback?: Function | object | string, thisArg?: any) => number;
+    findLastIndex: <T>(array: T[], predicate?: ((index: number, item: T, array: T[]) => any) | object | string, thisArg?: any) => number;
 
     makeArray: <T>(length: number, value?: T) => number[] | T[];