diff --git a/Adapter.hxx b/Adapter.hxx
index d41a3c0..fe5ce53 100644
--- a/Adapter.hxx
+++ b/Adapter.hxx
@@ -1,3 +1,6 @@
+// This file is under GNU General Public License 3.0
+// see LICENSE.txt
+
 #pragma once
 
 #include <thread>