diff --git a/src/libcamera/message.cpp b/src/libcamera/message.cpp
index 0580c105..9f22ad7f 100644
--- a/src/libcamera/message.cpp
+++ b/src/libcamera/message.cpp
@@ -41,6 +41,8 @@ LOG_DEFINE_CATEGORY(Message)
  * \brief The message type
  * \var Message::None
  * \brief Invalid message type
+ * \var Message::SignalMessage
+ * \brief Asynchronous signal delivery across threads
  */
 
 /**