diff --git a/src/internal/observable/fromEvent.ts b/src/internal/observable/fromEvent.ts
index 6b3d7e8003..a5ad471fa6 100644
--- a/src/internal/observable/fromEvent.ts
+++ b/src/internal/observable/fromEvent.ts
@@ -2,6 +2,8 @@ import { Observable } from '../Observable';
 import { isFunction } from '../util/isFunction';
 import { Subscriber } from '../Subscriber';
 
+const toString: Function = Object.prototype.toString;
+
 export type NodeStyleEventEmitter = {
   addListener: (eventName: string, handler: Function) => void;
   removeListener: (eventName: string, handler: Function) => void;