diff --git a/clinicadl/tsvtools/split/split.py b/clinicadl/tsvtools/split/split.py
index 158819f14..81ea7606f 100644
--- a/clinicadl/tsvtools/split/split.py
+++ b/clinicadl/tsvtools/split/split.py
@@ -281,8 +281,6 @@ def split_diagnoses(
 
     if categorical_split_variable is None:
         categorical_split_variable = "diagnosis"
-    else:
-        categorical_split_variable.append("diagnosis")
 
     # Read files
     diagnosis_df_path = data_tsv.name