diff --git a/packages/bun-types/bun-test.d.ts b/packages/bun-types/bun-test.d.ts
index 822617df53..06d7b7c172 100644
--- a/packages/bun-types/bun-test.d.ts
+++ b/packages/bun-types/bun-test.d.ts
@@ -31,7 +31,7 @@ declare module "bun:test" {
 
   interface Jest {
     restoreAllMocks(): void;
-    fn<T extends AnyFunction>(): Mock<T>;
+    fn<T extends AnyFunction>(func: T): Mock<T>;
   }
   export const jest: Jest;
   export namespace jest {