diff --git a/unit_tests/test_zaza_model.py b/unit_tests/test_zaza_model.py
index c8d0ec2..0a57bf8 100644
--- a/unit_tests/test_zaza_model.py
+++ b/unit_tests/test_zaza_model.py
@@ -1013,7 +1013,7 @@ disk_formats = ami,ari,aki,vhd,vmdk,raw,qcow2,vdi,iso,root-tar
         model.prepare_series_upgrade(_machine_num, to_series=_to_series)
         self.subprocess.check_call.assert_called_once_with(
             ["juju", "upgrade-series", "-m", self.model_name,
-             "prepare", _machine_num, _to_series, "--yes"])
+             _machine_num, "prepare", _to_series, "--yes"])
 
     def test_complete_series_upgrade(self):
         self.patch_object(model, 'get_juju_model',
@@ -1023,7 +1023,7 @@ disk_formats = ami,ari,aki,vhd,vmdk,raw,qcow2,vdi,iso,root-tar
         model.complete_series_upgrade(_machine_num)
         self.subprocess.check_call.assert_called_once_with(
             ["juju", "upgrade-series", "-m", self.model_name,
-             "complete", _machine_num])
+             _machine_num, "complete"])
 
     def test_set_series(self):
         self.patch_object(model, 'get_juju_model',
diff --git a/zaza/model.py b/zaza/model.py
index dc391b1..d90b7f7 100644
--- a/zaza/model.py
+++ b/zaza/model.py
@@ -1221,7 +1221,7 @@ def prepare_series_upgrade(machine_num, to_series="xenial"):
     """
     juju_model = get_juju_model()
     cmd = ["juju", "upgrade-series", "-m", juju_model,
-           "prepare", machine_num, to_series, "--yes"]
+           machine_num, "prepare", to_series, "--yes"]
     subprocess.check_call(cmd)
 
 
@@ -1239,7 +1239,7 @@ def complete_series_upgrade(machine_num):
     """
     juju_model = get_juju_model()
     cmd = ["juju", "upgrade-series", "-m", juju_model,
-           "complete", machine_num]
+           machine_num, "complete"]
     subprocess.check_call(cmd)