Unity-Technologies/UnityCsReference · error · ArgumentException

Input Prefab asset is not an asset object. Input asset: {pre

Error message

Input Prefab asset is not an asset object. Input asset: {prefabAsset.name}

What it means

Thrown by ThrowIfInvalidAssetForReplacePrefabInstance when EditorUtility.IsPersistent(prefabAsset) returns false — the object is a scene or runtime instance, not an asset stored in the AssetDatabase. Replace operations require a real Prefab asset as the replacement source.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:2225

        // Instantiates the given prefab in a given scene
        public static Object InstantiatePrefab(Object assetComponentOrGameObject, Scene destinationScene)
        {
            return InstantiatePrefab_internal(assetComponentOrGameObject, destinationScene, null);
        }

        public static Object InstantiatePrefab(Object assetComponentOrGameObject, Transform parent)
        {
            return InstantiatePrefab_internal(assetComponentOrGameObject, EditorSceneManager.GetTargetSceneForNewGameObjects(), parent);
        }

        internal static void ThrowIfInvalidAssetForReplacePrefabInstance(GameObject prefabAsset, InteractionMode action)
        {
            if (prefabAsset == null)
                throw new ArgumentNullException(nameof(prefabAsset));

            if (!EditorUtility.IsPersistent(prefabAsset))
                throw new ArgumentException("Input Prefab asset is not an asset object. Input asset: " + prefabAsset.name, nameof(prefabAsset));

            var assetPath = AssetDatabase.GetAssetPath(prefabAsset);
            if (assetPath.StartsWith("Library/"))
                throw new InvalidOperationException(string.Format("Cannot replace the Prefab instance since the Prefab Asset is invalid for instance replacement. Prefab Asset path: " + assetPath));

            // Recording undo does not handle missing scripts
            var gameObjectsWithInvalidScript = FindGameObjectsWithInvalidComponent(prefabAsset);
            if (action == InteractionMode.UserAction && gameObjectsWithInvalidScript.Count > 0)
                throw new InvalidOperationException(string.Format($"Cannot replace the Prefab instance with the Prefab Asset '{AssetDatabase.GetAssetPath(prefabAsset)}' because it has a missing script. GameObject '{gameObjectsWithInvalidScript[0].name}' in the Prefab Asset has a missing script."));
        }

        internal static void ThrowIfInvalidArgumentsForReplacePrefabInstance(GameObject prefabInstanceRoot, GameObject prefabAssetRoot, bool checkValidAsset, InteractionMode mode)
        {
            if (prefabInstanceRoot == null)
                throw new ArgumentNullException(nameof(prefabInstanceRoot));

            if (prefabAssetRoot == null)
                throw new ArgumentNullException(nameof(prefabAssetRoot));

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Pass the original Prefab asset reference (from AssetDatabase.LoadAssetAtPath), not a runtime instance.
2. Check EditorUtility.IsPersistent(obj) before calling the replace API.
3. If you only have an instance, resolve its source asset via PrefabUtility.GetCorrespondingObjectFromSource.

Example fix

// before
GameObject liveInstance = Instantiate(myPrefab);
ThrowIfInvalidAssetForReplacePrefabInstance(liveInstance, mode);
// after
GameObject asset = PrefabUtility.GetCorrespondingObjectFromSource(liveInstance);
// or: AssetDatabase.LoadAssetAtPath<GameObject>("Assets/x.prefab")
ThrowIfInvalidAssetForReplacePrefabInstance(asset, mode);

if (!EditorUtility.IsPersistent(prefabAsset))
{ Debug.LogError("Object is not an asset; load it from AssetDatabase."); return; }
PrefabUtility.ThrowIfInvalidAssetForReplacePrefabInstance(prefabAsset, mode);

static bool IsPersistentAsset(Object obj) =>
    obj != null && EditorUtility.IsPersistent(obj);

When it happens

Trigger: Passing a scene-level GameObject or an instantiated runtime object as the prefabAsset argument to a ReplacePrefabInstance operation.

Common situations: Developer passes an instantiated Prefab (from Instantiate or InstantiatePrefab) instead of the asset reference. Confusing a live scene object with the template asset. Forgetting that IsPersistent is only true for objects in the AssetDatabase.

Related errors

• Value cannot be null. (Parameter 'prefabAsset')
• Cannot replace the Prefab instance since the Prefab Asset is
• Cannot replace the Prefab instance with the Prefab Asset '{A
• prefabAssetRoot
• PrefabFamilyPopup is already open

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/1c0161e8bec0c694. Report an issue: GitHub.