diff --git a/dec8/argv.py b/dec8/argv.py
index 6d9a2a1..42387e5 100644
--- a/dec8/argv.py
+++ b/dec8/argv.py
@@ -100,7 +100,10 @@ class Invocation:
 			self.args[name] = None
 		
 		for name, (T, default, _) in self.action.kv_args.items():
-			self.args[name] = T(default)
+			if default is None:
+				self.args[name] = None
+			else:
+				self.args[name] = T(default)
 		
 		# process positional (mandatory) args
 		count_p_args = len(self.action.p_args)