diff --git a/bldr/config.py b/bldr/config.py
index 94a8a32..d3c6004 100644
--- a/bldr/config.py
+++ b/bldr/config.py
@@ -78,7 +78,7 @@ def __init__(self, *args: Any, **kwargs: Any):
 
         super().__init__(*args, **kwargs)
 
-    def parse_known_args(self, args: Optional[Sequence[str]] = None, namespace: Optional[argparse.Namespace] = None) -> Tuple[argparse.Namespace, List[str]]:
+    def parse_known_args(self, args: Optional[Sequence[str]] = None, namespace: None = None) -> Tuple[argparse.Namespace, List[str]]:
         if self.config_loader:
             self.set_defaults_from_config(args)
         return super().parse_known_args(args, namespace=None)