diff --git a/kamailio/registrar-role.cfg b/kamailio/registrar-role.cfg
index 1da60da..8e3b36b 100644
--- a/kamailio/registrar-role.cfg
+++ b/kamailio/registrar-role.cfg
@@ -89,6 +89,9 @@ route[ATTEMPT_AUTHORIZATION]
             xlog("L_INFO", "$ci|log|authenticating $Au via Kazoo query response");
         } else {
             xlog("L_INFO", "$ci|log|failed to query Kazoo for authentication credentials for $Au $si:$sp");
+            append_to_reply("Retry-After: 60\r\n");
+            sl_send_reply("500", "Retry Later");
+            exit;
         }
     }