diff --git a/dbus/dbus-gproxy.c b/dbus/dbus-gproxy.c

index 36d55f8..949a0a0 100644

--- a/dbus/dbus-gproxy.c

+++ b/dbus/dbus-gproxy.c

@@ -658,8 +658,15 @@ unassociate_proxies (gpointer key, gpointer val, gpointer user_data)

 	{

 	  if (!priv->for_owner)

 	    {

-	      g_assert (priv->associated);

-	      g_assert (priv->name_call == NULL);

+	      /* If a service appeared and then vanished very quickly,

+	       * it's conceivable we have an inflight request for

+	       * GetNameOwner here.  Cancel it.

+	       * https://bugs.freedesktop.org/show_bug.cgi?id=18573

+	       */

+	      if (priv->name_call)

+		dbus_g_proxy_cancel_call (manager->bus_proxy, priv->name_call);

+

+	      priv->name_call = NULL;

 	      priv->associated = FALSE;

 	      manager->unassociated_proxies = g_slist_prepend (manager->unassociated_proxies, proxy);