diff --git a/tests/unit/service_test.py b/tests/unit/service_test.py
index deef6a3bada..d5dbcbea6d0 100644
--- a/tests/unit/service_test.py
+++ b/tests/unit/service_test.py
@@ -81,7 +81,7 @@ def test_container_without_name(self):
         service = Service('db', self.mock_client, 'myproject', image='foo')
 
         assert [c.id for c in service.containers()] == ['1']
-        assert service.g_next_container_number() == 2
+        assert service._next_container_number() == 2
         assert service.get_container(1).id == '1'
 
     def test_get_volumes_from_container(self):