diff --git a/TODO b/TODO
index 8a68f8400..ccb5adf72 100644
--- a/TODO
+++ b/TODO
@@ -21,4 +21,10 @@
   Set them all to 1 initially. When a DSN is sent, clear the bit. Set
    the bit when the ack is received.
   Do anything special with sent but unacked packets? Maybe, so you can
-   retransmit them.
\ No newline at end of file
+   retransmit them.
+
+  Dosen't look like contiki ever uses 802.15.4 acking: grep ACKFRAME
+
+  not much point to implement it here unless you also plan to use in
+   in contiki (pretty substantial change to core Contiki).
+