diff --git a/genie_registry/clinical.py b/genie_registry/clinical.py
index e5a4244c..3c497edb 100644
--- a/genie_registry/clinical.py
+++ b/genie_registry/clinical.py
@@ -392,7 +392,7 @@ def preprocess(self, newpath):
             "sample is True and inClinicalDb is True"
         )
         sample_cols = sample_cols_table.asDataFrame()["fieldName"].tolist()
-        clinicalTemplate = pd.DataFrame(columns=set(patient_cols + sample_cols))
+        clinicalTemplate = pd.DataFrame(columns=list(set(patient_cols + sample_cols)))
         sample = True
         patient = True