diff --git a/writer/H5FDpoison_sec2.c b/writer/H5FDpoison_sec2.c
index ac2a5e4c..7dd99e45 100644
--- a/writer/H5FDpoison_sec2.c
+++ b/writer/H5FDpoison_sec2.c
@@ -1,3 +1,9 @@
+// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
+// SPDX-License-Identifier: GPL-3.0-only OR HDF5
+
+// This file may be used, modified, and distributed under either GPL-3.0-only
+// or the HDF5 license, at the recipient's option.
+
 #include "H5FDpoison_sec2.h"
 
 #include <errno.h>
diff --git a/writer/H5FDpoison_sec2.h b/writer/H5FDpoison_sec2.h
index d8d68636..5470080d 100644
--- a/writer/H5FDpoison_sec2.h
+++ b/writer/H5FDpoison_sec2.h
@@ -1,3 +1,9 @@
+// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
+// SPDX-License-Identifier: GPL-3.0-only OR HDF5
+
+// This file may be used, modified, and distributed under either GPL-3.0-only
+// or the HDF5 license, at the recipient's option.
+
 #ifndef H5FD_POISON_SEC2_H
 #define H5FD_POISON_SEC2_H