diff --git a/backend/pashub_fetcher/tests/test_core_files.py b/backend/pashub_fetcher/tests/test_core_files.py
index f87d8679..2b20803c 100644
--- a/backend/pashub_fetcher/tests/test_core_files.py
+++ b/backend/pashub_fetcher/tests/test_core_files.py
@@ -152,3 +152,14 @@ def test_core_file_for_prefix_returns_photopack() -> None:
 
     # Assert
     assert result == CoreFiles.PHOTOPACK
+
+
+def test_core_file_for_unknown_filename_returns_none() -> None:
+    # Arrange
+    filename = "unknown_document_123.pdf"
+
+    # Act
+    result = core_file_for(filename)
+
+    # Assert
+    assert result is None