diff --git a/scikit_longitudinal/data_preparation/elsa_handler.py b/scikit_longitudinal/data_preparation/elsa_handler.py
index e05dd5e..4a5caee 100644
--- a/scikit_longitudinal/data_preparation/elsa_handler.py
+++ b/scikit_longitudinal/data_preparation/elsa_handler.py
@@ -180,12 +180,15 @@ def save_datasets(self, dir_output: str = "tmp", file_format: str = "csv"):
                 dataset.to_csv(f"{dir_output}/{class_name}_dataset.csv", index=False)
             elif file_format.lower() == "arff":
                 dataset.fillna("?", inplace=True)
-                arff.dump(
-                    f"{dir_output}/{class_name}_dataset.arff",
-                    dataset.values,
-                    relation=class_name,
-                    names=dataset.columns,
-                )
+                arff_data = {
+                    'description': '',
+                    'relation': class_name,
+                    'attributes': [(col, 'REAL' if dataset[col].dtype in ['float64', 'int64'] else 'STRING') for col in
+                                   dataset.columns],
+                    'data': dataset.values.tolist()
+                }
+                with open(f"{dir_output}/{class_name}_dataset.arff", 'w') as f:
+                    arff.dump(arff_data, f)
             else:
                 raise ValueError(f"Unsupported file format: {file_format}")
 
diff --git a/scikit_longitudinal/data_preparation/longitudinal_dataset.py b/scikit_longitudinal/data_preparation/longitudinal_dataset.py
index 89f770c..b972d34 100644
--- a/scikit_longitudinal/data_preparation/longitudinal_dataset.py
+++ b/scikit_longitudinal/data_preparation/longitudinal_dataset.py
@@ -485,12 +485,13 @@ def convert(self, output_path: Union[str, Path]) -> None:  # pragma: no cover
 
         if file_ext == ".arff":
             arff_data = self._csv_to_arff(self._data, self.file_path.stem)
-            arff.dump(
-                output_path,
-                arff_data["data"],
-                relation=arff_data["relation"],
-                names=arff_data["attributes"],
-            )
+            with open(output_path, 'w') as f:
+                arff.dump({
+                    'description': '',
+                    'relation': arff_data['relation'],
+                    'attributes': arff_data['attributes'],
+                    'data': arff_data['data']
+                }, f)
         elif file_ext == ".csv":
             self._data.to_csv(output_path, index=False, na_rep="")
         else: