diff --git a/unittests/interface/interface_functions/test_virtual_machine_generator.py b/unittests/interface/interface_functions/test_virtual_machine_generator.py
index 4bca1e9b5e..6a7808d721 100644
--- a/unittests/interface/interface_functions/test_virtual_machine_generator.py
+++ b/unittests/interface/interface_functions/test_virtual_machine_generator.py
@@ -46,7 +46,7 @@ def test_by_set_chips(self):
         set_config("Machine", "version", 5)
         set_config("Machine", "virtual_board", "True")
         # Called by sim.setup
-        FecDataWriter.mock().set_n_chips_in_graph(None, 100)
+        FecDataWriter.mock().set_n_chips_in_graph(100)
         machine = virtual_machine_generator()
         self.assertEqual(3, len(machine.ethernet_connected_chips))