diff --git a/csst_common/file.py b/csst_common/file.py
index 0fd1aec5f5d595cdc70da9d57743141eec3f8b7c..b8cbaf0601681afa2348507bdae4ab5d5588c139 100644
--- a/csst_common/file.py
+++ b/csst_common/file.py
@@ -49,7 +49,7 @@ class File:
             r"(?P<exp_start>[0-9]{14})_"
             r"(?P<exp_stop>[0-9]{14})_"
             r"(?P<obs_id>[0-9]{11,14})_"
-            r"(?P<detector>[0-9]+)_"
+            r"(?P<detector>[0-9A-Z]+)_"
             r"L(?P<level>[0-9]{1})_"
             r"V(?P<version>[0-9]{2})"
             r"(?P<ext>[a-z.]+)"