diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index f4b7f854a5f..086b08eba54 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -1344,12 +1344,14 @@ nsGlobalWindow::~nsGlobalWindow()
 void
 nsGlobalWindow::AddEventTargetObject(DOMEventTargetHelper* aObject)
 {
+  MOZ_ASSERT(IsInnerWindow());
   mEventTargetObjects.PutEntry(aObject);
 }
 
 void
 nsGlobalWindow::RemoveEventTargetObject(DOMEventTargetHelper* aObject)
 {
+  MOZ_ASSERT(IsInnerWindow());
   mEventTargetObjects.RemoveEntry(aObject);
 }
 
diff --git a/dom/base/nsGlobalWindow.h b/dom/base/nsGlobalWindow.h
index d3bda51bf26..438508e4e5b 100644
--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -696,6 +696,7 @@ public:
 
   void UnmarkGrayTimers();
 
+  // Inner windows only.
   void AddEventTargetObject(mozilla::DOMEventTargetHelper* aObject);
   void RemoveEventTargetObject(mozilla::DOMEventTargetHelper* aObject);
 
diff --git a/dom/events/DOMEventTargetHelper.cpp b/dom/events/DOMEventTargetHelper.cpp
index 758852a62e0..503ddd4bb63 100644
--- a/dom/events/DOMEventTargetHelper.cpp
+++ b/dom/events/DOMEventTargetHelper.cpp
@@ -91,7 +91,7 @@ DOMEventTargetHelper::~DOMEventTargetHelper()
 void
 DOMEventTargetHelper::BindToOwner(nsPIDOMWindow* aOwner)
 {
-  MOZ_ASSERT(!aOwner || aOwner->IsInnerWindow());
+  MOZ_ASSERT_IF(aOwner, aOwner->IsInnerWindow());
   nsCOMPtr<nsIGlobalObject> glob = do_QueryInterface(aOwner);
   BindToOwner(glob);
 }
@@ -112,6 +112,7 @@ DOMEventTargetHelper::BindToOwner(nsIGlobalObject* aOwner)
     // Let's cache the result of this QI for fast access and off main thread usage
     mOwnerWindow = nsCOMPtr<nsPIDOMWindow>(do_QueryInterface(aOwner)).get();
     if (mOwnerWindow) {
+      MOZ_ASSERT(mOwnerWindow->IsInnerWindow());
       mHasOrHasHadOwnerWindow = true;
       static_cast<nsGlobalWindow*>(mOwnerWindow)->AddEventTargetObject(this);
     }
@@ -134,6 +135,7 @@ DOMEventTargetHelper::BindToOwner(DOMEventTargetHelper* aOther)
       // Let's cache the result of this QI for fast access and off main thread usage
       mOwnerWindow = nsCOMPtr<nsPIDOMWindow>(do_QueryInterface(mParentObject)).get();
       if (mOwnerWindow) {
+        MOZ_ASSERT(mOwnerWindow->IsInnerWindow());
         mHasOrHasHadOwnerWindow = true;
         static_cast<nsGlobalWindow*>(mOwnerWindow)->AddEventTargetObject(this);
       }
diff --git a/dom/events/DOMEventTargetHelper.h b/dom/events/DOMEventTargetHelper.h
index 3c70a0a352e..ef58e5b7d67 100644
--- a/dom/events/DOMEventTargetHelper.h
+++ b/dom/events/DOMEventTargetHelper.h
@@ -120,12 +120,8 @@ public:
   nsresult CheckInnerWindowCorrectness()
   {
     NS_ENSURE_STATE(!mHasOrHasHadOwnerWindow || mOwnerWindow);
-    if (mOwnerWindow) {
-      NS_ASSERTION(mOwnerWindow->IsInnerWindow(), "Should have inner window here!\n");
-      nsPIDOMWindow* outer = mOwnerWindow->GetOuterWindow();
-      if (!outer || outer->GetCurrentInnerWindow() != mOwnerWindow) {
-        return NS_ERROR_FAILURE;
-      }
+    if (mOwnerWindow && !mOwnerWindow->IsCurrentInnerWindow()) {
+      return NS_ERROR_FAILURE;
     }
     return NS_OK;
   }
@@ -159,7 +155,7 @@ protected:
 private:
   // Inner window or sandbox.
   nsIGlobalObject*           mParentObject;
-  // mParentObject pre QI-ed and cached
+  // mParentObject pre QI-ed and cached (inner window)
   // (it is needed for off main thread access)
   nsPIDOMWindow*             mOwnerWindow;
   bool                       mHasOrHasHadOwnerWindow;