diff --git a/include/osmocom/upf/up_peer.h b/include/osmocom/upf/up_peer.h
index 59c2b91..be5dd52 100644
--- a/include/osmocom/upf/up_peer.h
+++ b/include/osmocom/upf/up_peer.h
@@ -41,6 +41,7 @@ enum up_peer_event {
 };
 
 struct up_peer {
+	/* item in up_endpoint->peers */
 	struct llist_head entry;
 
 	struct osmo_fsm_inst *fi;