diff --git a/SAS/TMSS/backend/src/tmss/tmssapp/adapters/parset.py b/SAS/TMSS/backend/src/tmss/tmssapp/adapters/parset.py
index 7b06a3eb24c79a88f0e5ebf9db4b238f239929d2..137db75995ebe89bee636e85e41d28a24b97fbf5 100644
--- a/SAS/TMSS/backend/src/tmss/tmssapp/adapters/parset.py
+++ b/SAS/TMSS/backend/src/tmss/tmssapp/adapters/parset.py
@@ -448,7 +448,7 @@ def _convert_to_parset_dict_for_preprocessing_pipeline_schema(subtask: models.Su
     dppp_steps = []
     if spec["preflagger0"]["enabled"]:
         dppp_steps.append('preflagger[0]')
-        parset["Observation.ObservationControl.PythonControl.DPPP.preflagger[0].chan"] = "[%s]" % spec["preflagger0"]["channels"]
+        parset["Observation.ObservationControl.PythonControl.DPPP.preflagger[0].chan"] = spec["preflagger0"]["channels"].split(",")
         parset["Observation.ObservationControl.PythonControl.DPPP.preflagger[0].abstime"] = []
         parset["Observation.ObservationControl.PythonControl.DPPP.preflagger[0].azimuth"] = []
         parset["Observation.ObservationControl.PythonControl.DPPP.preflagger[0].baseline"] = ""