diff --git a/agentscore_commerce/checkout.py b/agentscore_commerce/checkout.py
index b131cd1..277f3a9 100644
--- a/agentscore_commerce/checkout.py
+++ b/agentscore_commerce/checkout.py
@@ -2413,7 +2413,26 @@ async def _run_wallet_sanctions_only(self, ctx: CheckoutContext) -> CheckoutResu
             )
 
         decision = result.get("decision") if isinstance(result, dict) else None
-        if decision == "deny":
+
+        # Fail closed on anything that is not an explicit allow. This branched on
+        # `decision == "deny"`, so every other value was permitted by structure:
+        # None from an unreadable response, and any decision the API adds later.
+        # This path is strict-liability wallet OFAC screening and already denies
+        # on an API outage above, so treating an unreadable answer as a pass
+        # contradicted its own posture.
+        if decision is None:
+            reason = DenialReason(
+                code="api_error",
+                message="assess returned no decision",
+            )
+            return CheckoutResult(
+                status=denial_reason_status(reason),
+                body=denial_reason_to_body(reason),
+                headers={},
+                reference_id=ctx.reference_id,
+                settled=False,
+            )
+        if decision != "allow":
             decision_reasons = result.get("decision_reasons") or [] if isinstance(result, dict) else []
             reason = DenialReason(
                 code="wallet_not_trusted",
diff --git a/agentscore_commerce/checkout_compute_first.py b/agentscore_commerce/checkout_compute_first.py
index 9ad835c..8716cc7 100644
--- a/agentscore_commerce/checkout_compute_first.py
+++ b/agentscore_commerce/checkout_compute_first.py
@@ -495,7 +495,17 @@ async def _enforce_wallet_sanctions(
 
         if denial_reason is None:
             decision = result.get("decision") if isinstance(result, dict) else None
-            if decision == "deny":
+            # Fail closed on anything that is not an explicit allow. This branched
+            # on `decision == "deny"`, so every other value was permitted by
+            # structure: None from an unreadable response, and any decision the
+            # API adds later. The except above already denies on an outage, so
+            # letting an unreadable answer through contradicted that posture.
+            if decision is None:
+                denial_reason = DenialReason(
+                    code="api_error",
+                    message="assess returned no decision",
+                )
+            elif decision != "allow":
                 decision_reasons = list(result.get("decision_reasons") or []) if isinstance(result, dict) else []
                 denial_reason = DenialReason(
                     code="wallet_not_trusted",
diff --git a/tests/test_checkout_compute_first_ofac.py b/tests/test_checkout_compute_first_ofac.py
index 9b1c4d4..59101ae 100644
--- a/tests/test_checkout_compute_first_ofac.py
+++ b/tests/test_checkout_compute_first_ofac.py
@@ -135,6 +135,59 @@ async def test_sdn_signer_denies_before_x402_settle(
     fake_server.verify_payment.assert_not_called()
 
 
+@pytest.mark.asyncio
+async def test_missing_decision_fails_closed(monkeypatch: pytest.MonkeyPatch) -> None:
+    """A response carrying no decision must DENY rather than settle.
+
+    This branched on `decision == "deny"`, so anything else was permitted by
+    structure, including None from an unreadable response. The except above
+    already denies on an outage, so letting an unreadable answer through
+    contradicted that posture, and here it would have settled a payment.
+    """
+    monkeypatch.setenv("AGENTSCORE_API_KEY", "ask_test_key")
+    fake_server = _make_fake_x402_server()
+    checkout = ComputeFirstCheckout(
+        name="search",
+        url="https://api.example.com/search",
+        unit_price_cents=1,
+        rails=_make_rails(),
+        x402_server=fake_server,
+        run_work=_run_one,
+    )
+    await checkout.handle(_req(body={"q": "x"}))
+    with patch(
+        "agentscore_commerce.api.AgentScore.aassess",
+        new=AsyncMock(return_value={"decision_reasons": []}),
+    ):
+        result = await checkout.handle(_req(headers={"x-payment": _x402_header()}, body={"q": "x"}))
+    assert result[1]["error"]["code"] == "api_error"
+    fake_server.verify_payment.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_unrecognised_decision_fails_closed(monkeypatch: pytest.MonkeyPatch) -> None:
+    """A decision value we do not know is not an approval either."""
+    monkeypatch.setenv("AGENTSCORE_API_KEY", "ask_test_key")
+    fake_server = _make_fake_x402_server()
+    checkout = ComputeFirstCheckout(
+        name="search",
+        url="https://api.example.com/search",
+        unit_price_cents=1,
+        rails=_make_rails(),
+        x402_server=fake_server,
+        run_work=_run_one,
+    )
+    await checkout.handle(_req(body={"q": "x"}))
+    with patch(
+        "agentscore_commerce.api.AgentScore.aassess",
+        new=AsyncMock(return_value={"decision": "review", "decision_reasons": []}),
+    ):
+        result = await checkout.handle(_req(headers={"x-payment": _x402_header()}, body={"q": "x"}))
+    assert result[0] == 403
+    assert result[1]["error"]["code"] == "wallet_not_trusted"
+    fake_server.verify_payment.assert_not_called()
+
+
 @pytest.mark.asyncio
 async def test_clean_signer_continues_to_settle(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setenv("AGENTSCORE_API_KEY", "ask_test_key")
diff --git a/tests/test_checkout_wallet_ofac_default.py b/tests/test_checkout_wallet_ofac_default.py
index 697daec..d0d89ff 100644
--- a/tests/test_checkout_wallet_ofac_default.py
+++ b/tests/test_checkout_wallet_ofac_default.py
@@ -124,6 +124,57 @@ async def test_clean_signer_with_no_gate_allows_settle_to_proceed(
     assert result.status != 403 or "wallet_not_trusted" not in str(result.body)
 
 
+@pytest.mark.asyncio
+@respx.mock
+async def test_missing_decision_fails_closed(monkeypatch: pytest.MonkeyPatch) -> None:
+    """A response carrying no decision must DENY, not fall through as an allow.
+
+    This branched on `decision == "deny"`, so every other value was permitted by
+    structure: None from an unreadable response, and any decision the API adds
+    later. This path is strict-liability wallet OFAC screening and already denies
+    on an API outage, so treating an unreadable answer as a pass contradicted its
+    own posture.
+    """
+    monkeypatch.setenv("AGENTSCORE_API_KEY", "ask_test_key")
+    respx.post(ASSESS_URL).mock(return_value=httpx.Response(200, json={"decision_reasons": []}))
+    checkout = _checkout(gate=None)
+    request = _req(headers={"x-payment": _x402_payment_header(SDN_WALLET)})
+    result = await checkout.handle(request)
+    assert result.settled is False
+    assert "api_error" in str(result.body)
+
+
+@pytest.mark.asyncio
+@respx.mock
+async def test_null_decision_fails_closed(monkeypatch: pytest.MonkeyPatch) -> None:
+    """An explicit null decision is the same unreadable case as a missing one."""
+    monkeypatch.setenv("AGENTSCORE_API_KEY", "ask_test_key")
+    respx.post(ASSESS_URL).mock(return_value=httpx.Response(200, json={"decision": None, "decision_reasons": []}))
+    checkout = _checkout(gate=None)
+    request = _req(headers={"x-payment": _x402_payment_header(SDN_WALLET)})
+    result = await checkout.handle(request)
+    assert result.settled is False
+    assert "api_error" in str(result.body)
+
+
+@pytest.mark.asyncio
+@respx.mock
+async def test_unrecognised_decision_fails_closed(monkeypatch: pytest.MonkeyPatch) -> None:
+    """A decision value we do not know is not an approval either.
+
+    Guards the forward case: adding a decision on the API side must not silently
+    open this gate on an already-released SDK.
+    """
+    monkeypatch.setenv("AGENTSCORE_API_KEY", "ask_test_key")
+    _mock_assess("review", reasons=[])
+    checkout = _checkout(gate=None)
+    request = _req(headers={"x-payment": _x402_payment_header(SDN_WALLET)})
+    result = await checkout.handle(request)
+    assert result.status == 403
+    assert result.settled is False
+    assert "wallet_not_trusted" in str(result.body)
+
+
 @pytest.mark.asyncio
 async def test_no_api_key_logs_warn_once_and_skips(
     monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture