diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index bdf2ad7..6c6a1fb 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -296,6 +296,7 @@
 	if (smpp_first) {
 		rc = smpp_try_deliver(gsms, conn, deferred);
 		if (rc == GSM411_RP_CAUSE_MO_NUM_UNASSIGNED)
+			/* unknown subscriber, try local */
 			goto try_local;
 		if (rc < 0) {
 	 		LOGP(DLSMS, LOGL_ERROR, "%s: SMS delivery error: %d.",