diff --git a/tests/unit/api/test_backtest_endpoint.py b/tests/unit/api/test_backtest_endpoint.py
index b6cd0ac..737f713 100644
--- a/tests/unit/api/test_backtest_endpoint.py
+++ b/tests/unit/api/test_backtest_endpoint.py
@@ -166,7 +166,8 @@ def test_replay_window_regime_gate_drops_unfavorable_session():
 # --------------------------------------------------------------------------
 # Test plan case 4: /api/backtest?days=9999 -> clamped
 # --------------------------------------------------------------------------
-def test_api_backtest_clamped_for_huge_days():
+def test_api_backtest_clamped_for_huge_days(monkeypatch):
+    monkeypatch.setenv("BACKTEST_MAX_SESSIONS", "45")   # cap is env-tunable (default 300)
     state = DashboardState("momentum")
     kind, status, payload = _get(state, "/api/backtest?days=9999")
     assert kind == "json" and status == 200