diff --git a/thunar/thunar-thumbnailer.c b/thunar/thunar-thumbnailer.c
index 5a10bf07ac733e0038e2507bc34ee8298665a588..14c8f02c8a7b30fcb20957ca7f64d9de8e3142d7 100644
--- a/thunar/thunar-thumbnailer.c
+++ b/thunar/thunar-thumbnailer.c
@@ -329,7 +329,8 @@ thunar_thumbnailer_queue_async_reply (GObject      *proxy,
 
   thumbnailer = THUNAR_THUMBNAILER (job->thumbnailer);
 
-  _thunar_return_if_fail (THUNAR_IS_THUMBNAILER (thumbnailer));
+  if (THUNAR_IS_THUMBNAILER (thumbnailer) == FALSE)
+    return;
 
   _thumbnailer_lock (thumbnailer);