diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index b776968ba3f4..0a7fa4c51b1f 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -9702,6 +9702,13 @@ nsresult nsDocShell::DoURILoad(nsDocShellLoadState* aLoadState,
     securityFlags |= nsILoadInfo::SEC_FORCE_INHERIT_PRINCIPAL;
   }
 
+  // Must never have a parent for TYPE_DOCUMENT loads
+  MOZ_ASSERT_IF(contentPolicyType == nsIContentPolicy::TYPE_DOCUMENT,
+                !mBrowsingContext->GetParent());
+  // Subdocuments must have a parent
+  MOZ_ASSERT_IF(contentPolicyType == nsIContentPolicy::TYPE_SUBDOCUMENT,
+                mBrowsingContext->GetParent());
+
   RefPtr<LoadInfo> loadInfo =
       (contentPolicyType == nsIContentPolicy::TYPE_DOCUMENT)
           ? new LoadInfo(loadingWindow, aLoadState->TriggeringPrincipal(),