diff --git a/docs/user-guide/brokers.md b/docs/user-guide/brokers.md
index 00f280b..84404c9 100644
--- a/docs/user-guide/brokers.md
+++ b/docs/user-guide/brokers.md
@@ -44,6 +44,7 @@ await broker.connect()
 - `7496` is the usual TWS live port
 - `4002` and `4001` are the usual paper/live IB Gateway ports
 - TWS or IB Gateway must be running with API access enabled before you connect
+- Submitted orders use `DAY` time in force so TWS presets do not change their duration.
 
 ## Alpaca
 
diff --git a/src/ml4t/live/brokers/ib.py b/src/ml4t/live/brokers/ib.py
index b0d3f14..d500825 100644
--- a/src/ml4t/live/brokers/ib.py
+++ b/src/ml4t/live/brokers/ib.py
@@ -659,6 +659,8 @@ def _create_ib_order(
         else:
             raise ValueError(f"Unsupported order type: {order_type}")
 
+        # Send a concrete TIF so TWS presets cannot change it after submission.
+        order.tif = "DAY"
         # Honor the caller's extended-hours intent (no-op before this was set).
         order.outsideRth = outside_rth
         return order
diff --git a/tests/unit/test_ib_broker.py b/tests/unit/test_ib_broker.py
index 08eafe4..568e6e9 100644
--- a/tests/unit/test_ib_broker.py
+++ b/tests/unit/test_ib_broker.py
@@ -499,6 +499,8 @@ async def test_submit_limit_order(self, mock_ib_class):
         assert order.quantity == 50
         assert order.order_type == OrderType.LIMIT
         assert order.limit_price == 150.0
+        _, ib_order = mock_ib.placeOrder.call_args.args
+        assert ib_order.tif == "DAY"
 
     @pytest.mark.asyncio
     @patch("ml4t.live.brokers.ib.IB")
@@ -713,6 +715,7 @@ async def test_submit_market_order_defaults_rth_only(self, mock_ib_class):
 
         _, ib_order = mock_ib.placeOrder.call_args.args
         assert ib_order.outsideRth is False
+        assert ib_order.tif == "DAY"
 
     @pytest.mark.asyncio
     @patch("ml4t.live.brokers.ib.IB")
diff --git a/tests/unit/test_provider_contract.py b/tests/unit/test_provider_contract.py
index fabe19f..cf9868e 100644
--- a/tests/unit/test_provider_contract.py
+++ b/tests/unit/test_provider_contract.py
@@ -226,7 +226,7 @@ def test_tampered_reported_contract_fails_closed(
     assert classification.reason == "reported contract does not match its evidence commit"
 
 
-def test_pending_candidate_preserves_v012_ib_contract() -> None:
+def test_ib_tif_change_invalidates_v012_evidence() -> None:
     repository = Path(__file__).resolve().parents[2]
     tag = subprocess.run(
         ["git", "cat-file", "-e", "v0.1.2^{commit}"],
@@ -238,4 +238,5 @@ def test_pending_candidate_preserves_v012_ib_contract() -> None:
         pytest.skip("v0.1.2 history is required")
     classification = _classification(repository, "ib", "v0.1.2", "HEAD")
 
-    assert classification.reusable is True
+    assert classification.reusable is False
+    assert "src/ml4t/live/brokers/ib.py" in classification.changed_inputs