diff --git a/src/argclass/__init__.py b/src/argclass/__init__.py
index 5213372..3876a88 100644
--- a/src/argclass/__init__.py
+++ b/src/argclass/__init__.py
@@ -119,7 +119,7 @@ def _prepare_field(ap: ArgumentParser, name: str, field_: Field):
 
 def argclass(cls):
     @classmethod
-    def parse_args(cls, argv):
+    def parse_args(cls, argv=None):
         ap = ArgumentParser()
         for name, field_ in cls.__dataclass_fields__.items():
             _prepare_field(ap, name, field_)