diff --git a/include/gds-render/output-renderers/external-renderer-interfaces.h b/include/gds-render/output-renderers/external-renderer-interfaces.h
index 7c2c589..d43736b 100644
--- a/include/gds-render/output-renderers/external-renderer-interfaces.h
+++ b/include/gds-render/output-renderers/external-renderer-interfaces.h
@@ -1,3 +1,22 @@
+/*
+ * GDSII-Converter
+ * Copyright (C) 2018  Mario Hüttel <mario.huettel@gmx.net>
+ *
+ * This file is part of GDSII-Converter.
+ *
+ * GDSII-Converter is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * GDSII-Converter is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GDSII-Converter.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
 #ifndef __EXTERNAL_RENDERER_INTERFACES_H__
 #define __EXTERNAL_RENDERER_INTERFACES_H__