diff --git a/zip-proportional-output-fee-mechanism-pofm.rst b/zip-proportional-output-fee-mechanism-pofm.rst
index d5ef7779..ce12d21a 100644
--- a/zip-proportional-output-fee-mechanism-pofm.rst
+++ b/zip-proportional-output-fee-mechanism-pofm.rst
@@ -65,7 +65,7 @@ transactions with 2 outputs.
 Requirements for gathering consensus
 -------------------------
 
-Wallet developers must update the fees to the proposed formula by Madars and 
+Wallet developers SHOULD update the fees to the proposed formula by Madars and 
 Kris Nuttycombe [#madars-1]_
 
 min_fee = base_fee * max(0, #inputs + #outputs - 4)