diff --git a/devtools/server/actors/replay/replay.js b/devtools/server/actors/replay/replay.js
index 903f6c3ac3fa..f0df221c162f 100644
--- a/devtools/server/actors/replay/replay.js
+++ b/devtools/server/actors/replay/replay.js
@@ -258,6 +258,7 @@ Services.obs.addObserver(
   {
     observe(subject, topic, data) {
       assert(topic == "webnavigation-create");
+      subject.QueryInterface(Ci.nsIDocShell);
       subject.watchedByDevtools = true;
     },
   },