diff --git a/unittests/operations_tests/routing_table_generator_tests/test_basic.py b/unittests/operations_tests/routing_table_generator_tests/test_basic.py
index 1d4d77b7c..0cb0fb122 100644
--- a/unittests/operations_tests/routing_table_generator_tests/test_basic.py
+++ b/unittests/operations_tests/routing_table_generator_tests/test_basic.py
@@ -13,7 +13,8 @@
 # limitations under the License.
 
 import unittest
-from typing import Optional
+from typing import Optional, cast
+from typing_extensions import Self
 from spinn_utilities.config_holder import set_config
 from pacman.config_setup import unittest_setup
 from pacman.data.pacman_data_writer import PacmanDataWriter
@@ -47,7 +48,7 @@ def __init__(
             n_atoms=n_atoms)
         self.__fixed_key_and_mask = fixed_key_and_mask
         self._splitter = SplitterOneAppOneMachine()
-        self._splitter.set_governed_app_vertex(self)
+        self._splitter.set_governed_app_vertex(cast(Self, self))
 
     def get_fixed_key_and_mask(
             self, partition_id: str) -> Optional[BaseKeyAndMask]: