diff --git a/backend/categorisation/tests/test_prioritised_plan_selected.py b/backend/categorisation/tests/test_prioritised_plan_selected.py
index 74eb8c69..7544eb9c 100644
--- a/backend/categorisation/tests/test_prioritised_plan_selected.py
+++ b/backend/categorisation/tests/test_prioritised_plan_selected.py
@@ -92,3 +92,24 @@ def test_cheapest_plan_returned_if_not_in_priority_list(
 
     # assert
     assert actual_default_plan.id == expected_default_plan_id
+
+
+def test_all_plans_zero_cost__highest_priority_returned(
+    created_at_datetime: datetime,
+) -> None:
+    # arrange
+    epc_c_plan = make_plan(created_at_datetime, True, cost_of_works=0.0, name="EPC C")
+    minor_works_plan = make_plan(
+        created_at_datetime, False, cost_of_works=0.0, name="EPC C - Minor Works"
+    )
+    scenario_priority_order: List[int] = [4, 3]
+    expected_default_plan_id = 2
+
+    # act
+    actual_default_plan = choose_cheapest_relevant_plan(
+        plans=[epc_c_plan, minor_works_plan],
+        scenario_priority_order=scenario_priority_order,
+    )
+
+    # assert
+    assert actual_default_plan.id == expected_default_plan_id