diff --git a/doc/Protocol.md b/doc/Protocol.md
index 83915e5e04428a217ec93b238530a11be271d1a1..90a1dfccf48b958dd049b3c4f7fdb44f1c667a41 100644
--- a/doc/Protocol.md
+++ b/doc/Protocol.md
@@ -1365,6 +1365,7 @@ TRUE
 * *Rule*: The sum of all inputs in `CommonBase` must equal the sum of all outputs in `CommonBase`
 
 > Functionally: we cannot create nor lose money through transactions. We can only transfer coins we own.
+> Functionally: also, we cannot convert a superiod unit base into a lower one.
 
 #### Global