diff --git a/lib/har-driver-actor.js b/lib/har-driver-actor.js
index afbc80e..e658f8a 100644
--- a/lib/har-driver-actor.js
+++ b/lib/har-driver-actor.js
@@ -159,6 +159,15 @@ var HarDriverActor = ActorClass(
       Ci.nsIWebProgress.NOTIFY_STATE_WINDOW |
       Ci.nsIWebProgress.NOTIFY_STATE_DOCUMENT;
 
+    let win = this.parent.originalWindow;
+
+    // Do not overwrite HAR object. It might be already there if
+    // autoConntect is on or there might be an existing object
+    // with the same on the page.
+    if (win.wrappedJSObject.HAR) {
+      return;
+    }
+
     // The client just attached to this actor, let's expose
     // HAR API to the content.
     this.parent.webProgress.addProgressListener(this, notifyMask);