diff --git a/js/xpconnect/loader/mozJSComponentLoader.cpp b/js/xpconnect/loader/mozJSComponentLoader.cpp
index 525d217ba290..7a71fbedbe32 100644
--- a/js/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/xpconnect/loader/mozJSComponentLoader.cpp
@@ -1372,6 +1372,9 @@ mozJSComponentLoader::Unload(const nsACString & aLocation)
         return NS_OK;
     }
 
+    MOZ_RELEASE_ASSERT(!mReuseLoaderGlobal, "Module unloading not supported when "
+                                            "compartment sharing is enabled");
+
     nsCOMPtr<nsIIOService> ioService = do_GetIOService(&rv);
     NS_ENSURE_SUCCESS(rv, rv);