diff --git a/draft-ietf-scitt-scrapi.md b/draft-ietf-scitt-scrapi.md
index 93ded0a..ffa3370 100644
--- a/draft-ietf-scitt-scrapi.md
+++ b/draft-ietf-scitt-scrapi.md
@@ -113,7 +113,7 @@ To facilitate automated response to errors, this document defines a set of stand
 
 Error responses SHOULD be sent with the `Content-Type: application/problem+json` HTTP header.
 
-As an example, submitting a Signed Statement with an unsupported signature algorithm would return a `400 Bad Request` status code and the following body:
+As an example, submitting a Signed Statement with an unsupported signature algorithm MUST return a `400 Bad Request` status code and the following body:
 
 ~~~json
 {