diff --git a/thunar/thunar-thumbnailer.c b/thunar/thunar-thumbnailer.c
index cfaf2c3d..69a2a7f0 100644
--- a/thunar/thunar-thumbnailer.c
+++ b/thunar/thunar-thumbnailer.c
@@ -331,6 +331,8 @@ thunar_thumbnailer_queue_async_reply (GObject      *proxy,
 
   _thunar_return_if_fail (THUNAR_IS_THUMBNAILER (thumbnailer));
 
+  thumbnailer = NULL;
+
   _thumbnailer_lock (thumbnailer);
 
   thunar_thumbnailer_dbus_call_queue_finish (THUNAR_THUMBNAILER_DBUS (proxy), &handle, res, &error);