diff --git a/zaza/charm_tests/test_utils.py b/zaza/charm_tests/test_utils.py
index 7e7e482..8235c42 100644
--- a/zaza/charm_tests/test_utils.py
+++ b/zaza/charm_tests/test_utils.py
@@ -142,7 +142,6 @@ class OpenStackBaseTest(unittest.TestCase):
         model.run_action(
             self.first_unit,
             'pause',
-            {},
             model_name=self.model_name)
         model.block_until_unit_wl_status(
             self.first_unit,
@@ -157,7 +156,6 @@ class OpenStackBaseTest(unittest.TestCase):
         model.run_action(
             self.first_unit,
             'resume',
-            {},
             model_name=self.model_name)
         model.block_until_unit_wl_status(
             self.first_unit,
diff --git a/zaza/model.py b/zaza/model.py
index b5c49cc..40faad4 100644
--- a/zaza/model.py
+++ b/zaza/model.py
@@ -434,15 +434,15 @@ get_status = sync_wrapper(async_get_status)
 
 
 async def async_run_action(unit_name, action_name, model_name=None,
-                           action_params=None):
+                           action_params={}):
     """Run action on given unit.
 
-    :param model_name: Name of model to query.
-    :type model_name: str
     :param unit_name: Name of unit to run action on
     :type unit_name: str
     :param action_name: Name of action to run
     :type action_name: str
+    :param model_name: Name of model to query.
+    :type model_name: str
     :param action_params: Dictionary of config options for action
     :type action_params: dict
     :returns: Action object