diff --git a/toolkit/xre/nsEmbedFunctions.cpp b/toolkit/xre/nsEmbedFunctions.cpp
index d48998246f7..b96c736a441 100644
--- a/toolkit/xre/nsEmbedFunctions.cpp
+++ b/toolkit/xre/nsEmbedFunctions.cpp
@@ -603,6 +603,7 @@ nsresult
 XRE_RunAppShell()
 {
     nsCOMPtr<nsIAppShell> appShell(do_GetService(kAppShellCID));
+    NS_ENSURE_TRUE(appShell, NS_ERROR_FAILURE);
 #if defined(XP_MACOSX)
     {
       // In content processes that want XPCOM (and hence want