diff --git a/sys/include/net/sock/async/types.h b/sys/include/net/sock/async/types.h
index f5bd149891..ee24db9940 100644
--- a/sys/include/net/sock/async/types.h
+++ b/sys/include/net/sock/async/types.h
@@ -1,3 +1,11 @@
+/*
+ * Copyright (C) 2019-20 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
 /**
  * @addtogroup      net_sock_async  Sock extension for asynchronous access
  *