diff --git a/tracker/tracker/src/main/app/observer/top_observer.ts b/tracker/tracker/src/main/app/observer/top_observer.ts
index 526270f54..d9f2d7f9d 100644
--- a/tracker/tracker/src/main/app/observer/top_observer.ts
+++ b/tracker/tracker/src/main/app/observer/top_observer.ts
@@ -77,6 +77,7 @@ export default class TopObserver extends Observer {
   private iframeObservers: IFrameObserver[] = []
   private handleIframe(iframe: HTMLIFrameElement): void {
     let doc: Document | null = null
+    let win: Window | null = null
     // setTimeout is required. Otherwise some event listeners (scroll, mousemove) applied in modules
     //     do not work on the iframe document when it 've been loaded dynamically ((why?))
     const handle = this.app.safe(() =>