Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c (revision 85764)
+++ channels/chan_sip.c (working copy)
@@ -14431,7 +14431,10 @@
        /* XXX Should we authenticate OPTIONS? XXX */
        if (ast_strlen_zero(p->context))
                ast_string_field_set(p, context, default_context);
-       if (res < 0)
+
+       if (ast_shutting_down())
+               transmit_response_with_allow(p, "503 Unavailable", req, 0);
+       else if (res < 0)
                transmit_response_with_allow(p, "404 Not Found", req, 0);
        else
                transmit_response_with_allow(p, "200 OK", req, 0);