diff --git a/types/event-emitter/index.d.ts b/types/event-emitter/index.d.ts
index 1b5fb29c62..6cb71999e2 100644
--- a/types/event-emitter/index.d.ts
+++ b/types/event-emitter/index.d.ts
@@ -15,6 +15,6 @@ declare namespace ee {
     }
 }
 
-declare function ee(obj: any): ee.Emitter;
+declare function ee(obj?: any): ee.Emitter;
 
 export = ee;