diff --git a/argdantic/core.py b/argdantic/core.py
index b3ae056..e11ee52 100644
--- a/argdantic/core.py
+++ b/argdantic/core.py
@@ -11,6 +11,8 @@
 from argdantic.parsing import Argument
 from argdantic.stores import SettingsStoreCallable
 
+SettingSourceCallable = Callable[[Type[BaseSettings]], PydanticBaseSettingsSource]
+
 
 class Command:
     """
@@ -231,8 +233,8 @@ def command(
         self,
         name: Optional[str] = None,
         help: Optional[str] = None,
-        sources: List[PydanticBaseSettingsSource] = None,
-        stores: List[SettingsStoreCallable] = None,
+        sources: Optional[List[SettingSourceCallable]] = None,
+        stores: Optional[List[SettingsStoreCallable]] = None,
         singleton: bool = False,
     ) -> Callable:
         """Decorator to register a function as a command.