diff --git a/csst_common/status.py b/csst_common/status.py
index b256806acdcf16bbe81e11a38fa18edc601e6232..3bb4cde7469def3244d82a14a238197d5d62d500 100644
--- a/csst_common/status.py
+++ b/csst_common/status.py
@@ -44,13 +44,15 @@ class CsstResult:
     def __init__(
         self,
         status: CsstStatus = CsstStatus.ERROR,
-        files: Optional[list] = None,
+        files: Optional[list[str]] = None,
         **output: Any,
     ):
         if files is None:
             files = []
         assert isinstance(status, CsstStatus)
-        assert type(files) is list
+        assert isinstance(files, list)
+        for _ in files:
+            assert isinstance(_, str)
         self.status: CsstStatus = status
         self.files: Optional[list] = files
         self.output: dict = output