diff --git a/src/transformers/hf_argparser.py b/src/transformers/hf_argparser.py
index b9e6f99b041d..b65edd1a5d72 100644
--- a/src/transformers/hf_argparser.py
+++ b/src/transformers/hf_argparser.py
@@ -181,9 +181,10 @@ def _parse_dataclass_field(parser: ArgumentParser, field: dataclasses.Field):
                 origin_type = getattr(field.type, "__origin__", field.type)
             elif bool not in field.type.__args__:
                 # filter `NoneType` in Union (except for `Union[bool, NoneType]`)
-                field.type = (
-                    field.type.__args__[0] if isinstance(None, field.type.__args__[1]) else field.type.__args__[1]
-                )
+                if str in field.type.__args__ and len(field.type.__args__) > 2:
+                    field.type = str
+                else:
+                    field.type = next(arg for arg in field.type.__args__ if arg is not type(None))
                 origin_type = getattr(field.type, "__origin__", field.type)
 
         # A variable to store kwargs for a boolean field, if needed