diff --git a/tests/backend/app/modelling/test_trigger_run_router.py b/tests/backend/app/modelling/test_trigger_run_router.py
index d383fae1d..9da1405f2 100644
--- a/tests/backend/app/modelling/test_trigger_run_router.py
+++ b/tests/backend/app/modelling/test_trigger_run_router.py
@@ -114,6 +114,23 @@ def test_trigger_run_rejects_a_task_that_already_has_subtasks(api: Api) -> None:
     assert len(api.subtasks_for(task)) == 1
 
 
+def test_trigger_run_rejects_filters_that_match_no_properties(api: Api) -> None:
+    """Zero resolved properties is a caller error (ADR-0055): a task with no
+    sub_tasks could never roll up to complete, and the app's preview shows the
+    same zero from the same rule before POSTing."""
+    # arrange — a portfolio with no properties at all
+    task = api.seed_task()
+    scenario = api.seed_scenario()
+
+    # act
+    response = _trigger(api, task, [scenario])
+
+    # assert
+    assert response.status_code == 400
+    assert api.sent_bodies == []
+    assert api.subtasks_for(task) == []
+
+
 def test_trigger_run_fans_out_one_subtask_and_message_per_scenario_batch(
     api: Api,
 ) -> None: