diff --git a/buds/06.md b/buds/06.md
index e79b418..a3bbe16 100644
--- a/buds/06.md
+++ b/buds/06.md
@@ -35,7 +35,7 @@ Example response from the server if the upload can be done:
 HTTP/1.1 200 OK
 ```
 
-If the upload cannot proceed, the server `MUST` return an appropriate HTTP status code and a custom header `X-Upload-Message` with a human readable error message.
+If the upload cannot proceed, the server `MUST` return an appropriate `4xx` HTTP status code and a custom header `X-Upload-Message` with a human readable error message.
 
 Some examples of error messages: