diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index 561ae0631a..12b58fa518 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -2466,6 +2466,7 @@ public class MessageHelper {
             byte[] key = Base64.decode(p, Base64.DEFAULT);
             byte[] signature = Base64.decode(s, Base64.DEFAULT);
 
+            // https://datatracker.ietf.org/doc/html/rfc8463
             if ("Ed25519".equals(salgo)) {
                 if (false) {
                     // https://www.rfc-editor.org/rfc/rfc8037#page-9