diff --git a/backend/tests/data/issued_at_cases.yaml b/backend/tests/data/issued_at_cases.yaml
index 8e58004..f00aa4d 100644
--- a/backend/tests/data/issued_at_cases.yaml
+++ b/backend/tests/data/issued_at_cases.yaml
@@ -1,3 +1,5 @@
+# Derived test cases from the Paperless-ngx project (https://github.com/paperless-ngx/paperless-ngx).
+# Copyright (c) Paperless-ngx contributors, licensed under the GNU GPL-3.0.
 cases:
   - name: date_format_1
     parser: parse_date