diff --git a/backend/tests/test_aio_sandbox_local_backend.py b/backend/tests/test_aio_sandbox_local_backend.py
index 62aaace50..4394b776a 100644
--- a/backend/tests/test_aio_sandbox_local_backend.py
+++ b/backend/tests/test_aio_sandbox_local_backend.py
@@ -323,6 +323,7 @@ def test_start_container_brackets_bare_ipv6_bind_override(monkeypatch):
 
 
 def test_start_container_binds_dood_port_to_bridge_gateway(monkeypatch):
+    """Force resolver failure so host DNS cannot bypass the bridge-gateway fallback."""
     backend = LocalContainerBackend(
         image="sandbox:latest",
         base_port=8080,
@@ -332,6 +333,10 @@ def test_start_container_binds_dood_port_to_bridge_gateway(monkeypatch):
     )
     monkeypatch.setenv("DEER_FLOW_SANDBOX_HOST", "host.docker.internal")
     monkeypatch.delenv("DEER_FLOW_SANDBOX_BIND_HOST", raising=False)
+    monkeypatch.setattr(
+        "deerflow.community.aio_sandbox.local_backend._resolve_sandbox_host_address",
+        lambda host: None,
+    )
     monkeypatch.setattr(
         "deerflow.community.aio_sandbox.local_backend._docker_bridge_gateway_ip",
         lambda: "172.17.0.1",