diff --git a/src/devices/sound/huc6230.cpp b/src/devices/sound/huc6230.cpp
index ce5ee4b3e2e..07fe59514ed 100644
--- a/src/devices/sound/huc6230.cpp
+++ b/src/devices/sound/huc6230.cpp
@@ -8,6 +8,9 @@
     - Volume is linear?
     - Make it actually working
     - Implement CDDA Volume
+
+    Related patent:
+    - https://patents.google.com/patent/US5692099
 */
 
 #include "emu.h"