diff --git a/tests/test_aux_power.py b/tests/test_aux_power.py
new file mode 100644
index 0000000..d73bc3f
--- /dev/null
+++ b/tests/test_aux_power.py
@@ -0,0 +1,18 @@
+from reactor_sim.reactor import Reactor
+from reactor_sim.commands import ReactorCommand
+
+
+def test_pump_stays_off_without_aux_power():
+    reactor = Reactor.default()
+    state = reactor.initial_state()
+    reactor.shutdown = False
+    reactor.primary_pump_active = True
+    reactor.primary_pump_units = [True, False]
+    reactor.secondary_pump_active = False
+    reactor.generator_auto = False
+    reactor.turbine_unit_active = [False, False, False]
+
+    reactor.step(state, dt=1.0, command=ReactorCommand(primary_pumps={1: True}))
+
+    assert state.primary_loop.mass_flow_rate == 0.0
+    assert state.primary_pumps[0].status in {"OFF", "STOPPING"}