diff --git a/master/master.c b/master/master.c
index 6d3da813..5aedb615 100644
--- a/master/master.c
+++ b/master/master.c
@@ -1348,8 +1348,8 @@ ec_slave_config_t *ecrt_master_slave_config(ec_master_t *master,
                 alias, position, vendor_id, product_code);
 
         // try to find the addressed slave
-        ec_slave_config_attach(sc);
-        ec_slave_config_load_default_assignment(sc);
+        if (!ec_slave_config_attach(sc))
+            ec_slave_config_load_default_assignment(sc);
 
         list_add_tail(&sc->list, &master->configs);
     }