diff --git a/IETF-RFC.md b/IETF-RFC.md
index 83f04e1d..d467a0b6 100644
--- a/IETF-RFC.md
+++ b/IETF-RFC.md
@@ -1294,6 +1294,9 @@ format:
 }
 ```
 
+A Directory Service MUST sign its responses using httpsig [RFC9421], so
+clients can verify the authenticity of the response.
+
 # Acknowledgements
 
 Our deepest thanks and appreciation go to the people who started the