diff --git a/src/langbot/pkg/plugin/connector.py b/src/langbot/pkg/plugin/connector.py
index cd07565aa..f2dbff418 100644
--- a/src/langbot/pkg/plugin/connector.py
+++ b/src/langbot/pkg/plugin/connector.py
@@ -841,6 +841,8 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
             runtime_id=self._runtime_id,
         )
         self.worker_policy = self._load_worker_policy()
+        plugin_config = self.ap.instance_config.data.get('plugin', {})
+        connect_timeout_seconds = self._runtime_connect_timeout(plugin_config)
 
         async with self._lifecycle_lock:
             if self._closing:
@@ -981,7 +983,6 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
                 task_coro = self.ctrl.run(new_connection_callback)
 
             self._transport_task = asyncio.create_task(task_coro)
-            connect_timeout_seconds = self._runtime_connect_timeout(self.ap.instance_config.data.get('plugin', {}))
             try:
                 await asyncio.wait_for(self._connected.wait(), timeout=connect_timeout_seconds)
             except asyncio.TimeoutError as exc:
diff --git a/tests/unit_tests/plugin/test_connector_ping.py b/tests/unit_tests/plugin/test_connector_ping.py
index c33f4012a..3b3aee016 100644
--- a/tests/unit_tests/plugin/test_connector_ping.py
+++ b/tests/unit_tests/plugin/test_connector_ping.py
@@ -132,6 +132,49 @@ async def test_stdio_runtime_connection_does_not_capture_unconsumed_stderr(
     await connector.aclose()
 
 
+@pytest.mark.asyncio
+async def test_invalid_connect_timeout_is_rejected_before_transport_startup(
+    monkeypatch: pytest.MonkeyPatch,
+):
+    connector = make_connector()
+    connector.ap.instance_config.data['plugin']['connect_timeout_seconds'] = 0
+    stdio_controller = Mock()
+    websocket_controller = Mock()
+    create_task = Mock()
+    get_platform = Mock(return_value='linux')
+    use_websocket = Mock(return_value=False)
+    connector._start_runtime_subprocess = AsyncMock()
+    monkeypatch.setattr(connector_module.constants, 'instance_id', 'instance-a')
+    monkeypatch.setattr(connector_module.asyncio, 'create_task', create_task)
+    monkeypatch.setattr(connector_module.platform, 'get_platform', get_platform)
+    monkeypatch.setattr(
+        connector_module.platform,
+        'use_websocket_to_connect_plugin_runtime',
+        use_websocket,
+    )
+    monkeypatch.setattr(
+        connector_module.stdio_client_controller,
+        'StdioClientController',
+        stdio_controller,
+    )
+    monkeypatch.setattr(
+        connector_module.ws_client_controller,
+        'WebSocketClientController',
+        websocket_controller,
+    )
+
+    with pytest.raises(ValueError, match='plugin.connect_timeout_seconds'):
+        await connector.initialize()
+
+    get_platform.assert_not_called()
+    use_websocket.assert_not_called()
+    stdio_controller.assert_not_called()
+    websocket_controller.assert_not_called()
+    connector._start_runtime_subprocess.assert_not_awaited()
+    create_task.assert_not_called()
+    assert connector._transport_task is None
+
+
 @pytest.mark.asyncio
 async def test_runtime_disconnect_notifies_once_and_clears_handler(
     monkeypatch: pytest.MonkeyPatch,