diff --git a/TODO b/TODO
index 4fa93945..f6de929c 100644
--- a/TODO
+++ b/TODO
@@ -43,6 +43,7 @@ Version 1.5.0:
 * Fix casting away constness during expected WC calculation.
 * Read AL status code on spontaneous state change.
 * Fix clearing domains etc. when not activated and releasing.
+* Output -EPROTO if mailbox protocol is not supported.
 
 Future issues: