diff --git a/dom/ipc/jsactor/JSWindowActorProtocol.cpp b/dom/ipc/jsactor/JSWindowActorProtocol.cpp
index b89c70236d16..530a475ab129 100644
--- a/dom/ipc/jsactor/JSWindowActorProtocol.cpp
+++ b/dom/ipc/jsactor/JSWindowActorProtocol.cpp
@@ -205,7 +205,17 @@ NS_IMETHODIMP JSWindowActorProtocol::Observe(nsISupports* aSubject,
 
   if (!inner) {
     nsCOMPtr<nsPIDOMWindowOuter> outer = do_QueryInterface(aSubject);
-    if (NS_WARN_IF(!outer) || NS_WARN_IF(!outer->GetCurrentInnerWindow())) {
+    if (NS_WARN_IF(!outer)) {
+      nsContentUtils::LogSimpleConsoleError(
+          NS_ConvertUTF8toUTF16(nsPrintfCString(
+              "JSWindowActor %s: expected window subject for topic '%s'.",
+              mName.get(), aTopic)),
+          "JSActor",
+          /* aFromPrivateWindow */ false,
+          /* aFromChromeContext */ true);
+      return NS_ERROR_FAILURE;
+    }
+    if (NS_WARN_IF(!outer->GetCurrentInnerWindow())) {
       return NS_ERROR_FAILURE;
     }
     wgc = outer->GetCurrentInnerWindow()->GetWindowGlobalChild();
diff --git a/dom/ipc/tests/JSWindowActor/browser_observer_notification.js b/dom/ipc/tests/JSWindowActor/browser_observer_notification.js
index 6a7691409f0f..ae8c40f78179 100644
--- a/dom/ipc/tests/JSWindowActor/browser_observer_notification.js
+++ b/dom/ipc/tests/JSWindowActor/browser_observer_notification.js
@@ -49,6 +49,25 @@ declTest("test observers with null data", {
 
 declTest("observers don't notify with wrong window", {
   async test(browser) {
+    const MSG_RE = /JSWindowActor TestWindow: expected window subject for topic 'test-js-window-actor-child-observer'/;
+    let expectMessage = new Promise(resolve => {
+      Services.console.registerListener(function consoleListener(msg) {
+        // Run everything async in order to avoid logging messages from the
+        // console listener.
+        Cu.dispatch(() => {
+          if (!MSG_RE.test(msg.message)) {
+            info("ignoring non-matching console message: " + msg.message);
+            return;
+          }
+          info("received console message: " + msg.message);
+          is(msg.logLevel, Ci.nsIConsoleMessage.error, "should be an error");
+
+          Services.console.unregisterListener(consoleListener);
+          resolve();
+        });
+      });
+    });
+
     await SpecialPowers.spawn(browser, [], async function() {
       const TOPIC = "test-js-window-actor-child-observer";
       Services.obs.notifyObservers(null, TOPIC);
@@ -61,6 +80,8 @@ declTest("observers don't notify with wrong window", {
         "Should not receive wrong window's observer notification!"
       );
     });
+
+    await expectMessage;
   },
 });