diff --git a/miniupnpd/upnpevents.c b/miniupnpd/upnpevents.c
index 628aff8..1013eb1 100644
--- a/miniupnpd/upnpevents.c
+++ b/miniupnpd/upnpevents.c
@@ -112,7 +112,7 @@ newSubscriber(const char * eventurl, const char * callback, int callbacklen)
 	/* TODO: improve that */
 	strncpy(tmp->uuid, uuidvalue_igd, sizeof(tmp->uuid));
 	tmp->uuid[sizeof(tmp->uuid)-1] = '\0';
-	snprintf(tmp->uuid+37, 5, "%04lx", random() & 0xffff);
+	snprintf(tmp->uuid+sizeof(tmp->uuid)-5, 5, "%04lx", random() & 0xffff);
 	return tmp;
 }