diff --git a/python/mach/mach/dispatcher.py b/python/mach/mach/dispatcher.py
index 6a4916c0fa0c..71df28d298c8 100644
--- a/python/mach/mach/dispatcher.py
+++ b/python/mach/mach/dispatcher.py
@@ -230,7 +230,7 @@ class CommandAction(argparse.Action):
                 setattr(command_namespace, name, extra)
             else:
                 setattr(command_namespace, name, options.get('default', []))
-        elif extra:
+        elif extra and handler.cls.__name__ != 'DeprecatedCommands':
             raise UnrecognizedArgumentError(command, extra)
 
     def _handle_main_help(self, parser, verbose):