diff --git a/src/transformers/hf_argparser.py b/src/transformers/hf_argparser.py
index f6861212632..55836022546 100644
--- a/src/transformers/hf_argparser.py
+++ b/src/transformers/hf_argparser.py
@@ -66,9 +66,15 @@ class HfArgumentParser(ArgumentParser):
             typestring = str(field.type)
             for prim_type in (int, float, str):
                 for collection in (List,):
-                    if typestring == f"typing.Union[{collection[prim_type]}, NoneType]":
+                    if (
+                        typestring == f"typing.Union[{collection[prim_type]}, NoneType]"
+                        or typestring == f"typing.Optional[{collection[prim_type]}]"
+                    ):
                         field.type = collection[prim_type]
-                if typestring == f"typing.Union[{prim_type.__name__}, NoneType]":
+                if (
+                    typestring == f"typing.Union[{prim_type.__name__}, NoneType]"
+                    or typestring == f"typing.Optional[{prim_type.__name__}]"
+                ):
                     field.type = prim_type
 
             if isinstance(field.type, type) and issubclass(field.type, Enum):