diff --git a/index.bs b/index.bs
index eaeac7f95..0fbd027bc 100644
--- a/index.bs
+++ b/index.bs
@@ -3882,7 +3882,7 @@ It mirrors some fields of the {{PublicKeyCredential}} object returned by
 
         This mirrors the {{Credential/type}} field of {{PublicKeyCredential}}.
 
-        Note: if all {{PublicKeyCredentialDescriptor}} elements in {{PublicKeyCredentialRequestOptions/allowCredentials}} are ignored then that must result in an error since an empty {{PublicKeyCredentialRequestOptions/allowCredentials}} is semantically distinct.
+        Note: If all {{PublicKeyCredentialDescriptor}} elements in {{PublicKeyCredentialRequestOptions/allowCredentials}} are ignored then that MUST result in an error since an empty {{PublicKeyCredentialRequestOptions/allowCredentials}} is semantically distinct.
 
     :   <dfn>id</dfn>
     ::  This member contains the [=credential ID=] of the [=public key credential=] the caller is referring to.