diff --git a/libXISF_global.h b/libXISF_global.h
index 6183893..2637a73 100644
--- a/libXISF_global.h
+++ b/libXISF_global.h
@@ -1,3 +1,21 @@
+/************************************************************************
+ * LibXISF - library to load and save XISF files                        *
+ * Copyright (C) 2023 Dušan Poizl                                       *
+ *                                                                      *
+ * This program is free software: you can redistribute it and/or modify *
+ * it under the terms of the GNU General Public License as published by *
+ * the Free Software Foundation, either version 3 of the License, or    *
+ * (at your option) any later version.                                  *
+ *                                                                      *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.*
+ ************************************************************************/
+
 #ifndef LIBXISF_GLOBAL_H
 #define LIBXISF_GLOBAL_H
 
diff --git a/libxisf.cpp b/libxisf.cpp
index 399b7c4..f467995 100644
--- a/libxisf.cpp
+++ b/libxisf.cpp
@@ -1,3 +1,21 @@
+/************************************************************************
+ * LibXISF - library to load and save XISF files                        *
+ * Copyright (C) 2023 Dušan Poizl                                       *
+ *                                                                      *
+ * This program is free software: you can redistribute it and/or modify *
+ * it under the terms of the GNU General Public License as published by *
+ * the Free Software Foundation, either version 3 of the License, or    *
+ * (at your option) any later version.                                  *
+ *                                                                      *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.*
+ ************************************************************************/
+
 #include "libxisf.h"
 #include <unordered_map>
 #include <QXmlStreamReader>
diff --git a/libxisf.h b/libxisf.h
index 891dd00..1d83d67 100644
--- a/libxisf.h
+++ b/libxisf.h
@@ -1,3 +1,21 @@
+/************************************************************************
+ * LibXISF - library to load and save XISF files                        *
+ * Copyright (C) 2023 Dušan Poizl                                       *
+ *                                                                      *
+ * This program is free software: you can redistribute it and/or modify *
+ * it under the terms of the GNU General Public License as published by *
+ * the Free Software Foundation, either version 3 of the License, or    *
+ * (at your option) any later version.                                  *
+ *                                                                      *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.*
+ ************************************************************************/
+
 #ifndef LIBXISF_H
 #define LIBXISF_H