diff --git a/mistralclient/tests/unit/base.py b/mistralclient/tests/unit/base.py
index 32a0023d..b4f734ae 100644
--- a/mistralclient/tests/unit/base.py
+++ b/mistralclient/tests/unit/base.py
@@ -31,7 +31,7 @@ class BaseCommandTest(base.BaseTestCase):
         self.app = mock.Mock()
         self.client = self.app.client_manager.workflow_engine
 
-    def call(self, command, app_args=[], prog_name=''):
+    def call(self, command, app_args=(), prog_name=''):
         cmd = command(self.app, app_args)
 
         parsed_args = cmd.get_parser(prog_name).parse_args(app_args)