diff --git a/src/cal_tools/tools.py b/src/cal_tools/tools.py
index b922efd35cafb252681bc22cb82cd938e6bcbc24..48c780dd43dc7c4c783dd0b6646218686a522faa 100644
--- a/src/cal_tools/tools.py
+++ b/src/cal_tools/tools.py
@@ -997,7 +997,7 @@ def write_constants_fragment(
 
 def write_constants_fragment_extracal(
         out_folder: Path,
-        calib_data,
+        calib_data: 'extra.calibration.CalibrationData',
         caldb_root: Path,
 ):
     """Record calibration constants metadata to a fragment file.