diff --git a/src/extensions/hmac.rs b/src/extensions/hmac.rs
index 27da0f4..45e3b60 100644
--- a/src/extensions/hmac.rs
+++ b/src/extensions/hmac.rs
@@ -17,7 +17,10 @@ use rust_crypto::sha2::Sha256;
 use std::collections::BTreeMap;
 use std::io::Cursor;
 
-//#[deprecated]
+#[deprecated(
+    since = "0.4.2",
+    note = "Please use FidoAssertionRequest::with_extension(HmacSecret) instead"
+)]
 pub trait HmacExtension {
     fn extension_name() -> &'static str {
         "hmac-secret"
@@ -90,6 +93,7 @@ pub trait HmacExtension {
     }
 }
 
+#[allow(deprecated)]
 impl HmacExtension for FidoDevice {
     fn get_data(&mut self, salt: &[u8; 32], salt2: Option<&[u8; 32]>) -> FidoResult<Value> {
         Ok(HmacSecret::extension_input(self, salt, salt2)?)