# RefIdUnknown

> Special value, -1, used when the managed reference Id for an object is unknown, for example if ManagedReferenceUtility.GetManagedReferenceIdForObject is called with invalid arguments.

## Definition

* **Type:** Field
* **Namespace:** [UnityEngine.Serialization](/engine/6000.0/script-reference/unityengine/serialization.md)
* **Assembly:** UnityEngine.CoreModule

```csharp
public const long RefIdUnknown = -1
```