diff --git a/57.md b/57.md
index 3f55e57ba2..c37126e889 100644
--- a/57.md
+++ b/57.md
@@ -132,7 +132,7 @@ The following should be true of the `zap receipt` event:
 - `tags` MUST include the `p` tag (zap recipient) AND optional `e` tag from the `zap request` AND optional `a` tag from the `zap request` AND optional `P` tag from the pubkey of the zap request (zap sender).
 - The `zap receipt` MUST have a `bolt11` tag containing the description hash bolt11 invoice.
 - The `zap receipt` MUST contain a `description` tag which is the JSON-encoded zap request.
-- `SHA256(description)` MUST match the description hash in the bolt11 invoice.
+- `SHA256(description)` SHOULD match the description hash in the bolt11 invoice.
 - The `zap receipt` MAY contain a `preimage` tag to match against the payment hash of the bolt11 invoice. This isn't really a payment proof, there is no real way to prove that the invoice is real or has been paid. You are trusting the author of the `zap receipt` for the legitimacy of the payment.
 
 The `zap receipt` is not a proof of payment, all it proves is that some nostr user fetched an invoice. The existence of the `zap receipt` implies the invoice as paid, but it could be a lie given a rogue implementation.