diff --git a/walledeval/data/core.py b/walledeval/data/core.py
index d536649..f3a3e8b 100644
--- a/walledeval/data/core.py
+++ b/walledeval/data/core.py
@@ -108,7 +108,7 @@ def from_csv(cls, filenames: Union[str, list[str]], **csv_kwargs):
     
     @classmethod
     def from_json(cls, filenames: Union[str, list[str]], **json_kwargs):
-        [filenames] if isinstance(filenames, str) else filenames
+        filenames = [filenames] if isinstance(filenames, str) else filenames
         dataset = load_dataset(
             "json", 
             data_files=filenames,
@@ -223,9 +223,10 @@ def from_list(cls, name: str, lst: list[dict], model: type = Prompt):
     
     @classmethod
     def from_csv(cls, filenames: Union[str, list[str]], model: type = Prompt, **csv_kwargs):
+        filenames = [filenames] if isinstance(filenames, str) else filenames
         dataset = load_dataset(
             "csv", 
-            data_files=[filenames] if isinstance(filenames, str) else filenames,
+            data_files=filenames,
             **csv_kwargs
         )['train']
         
@@ -237,9 +238,10 @@ def from_csv(cls, filenames: Union[str, list[str]], model: type = Prompt, **csv_
     
     @classmethod
     def from_json(cls, filenames: Union[str, list[str]], model: type = Prompt, **json_kwargs):
+        filenames = [filenames] if isinstance(filenames, str) else filenames
         dataset = load_dataset(
             "json", 
-            data_files=[filenames] if isinstance(filenames, str) else filenames,
+            data_files=filenames,
             **json_kwargs
         )['train']