Unity-Technologies/UnityCsReference · error · ArgumentException

Provided GameObject is not a Prefab instance

Error message

Provided GameObject is not a Prefab instance

What it means

PrefabOverridesUtility.ThrowExceptionIfNullOrNotPartOfPrefabInstance is the precondition guard called by GetObjectOverrides and related methods. It throws ArgumentException("Provided GameObject is not a Prefab instance") when the passed GameObject is not part of a prefab instance (i.e., PrefabUtility.IsPartOfPrefabInstance returns false). This covers both plain scene objects and prefab assets, since overrides only exist on prefab instances.

Source

Thrown at Editor/Mono/Prefabs/PrefabOverrides/PrefabOverridesUtility.cs:25

using UnityEngine;
using Unity.Scripting.LifecycleManagement;

namespace UnityEditor.SceneManagement
{
    internal class PrefabOverridesUtility
    {
        [NoAutoStaticsCleanup] // Reusable scratch buffer, always Clear()ed before and after use; holds no live references across reload.
        static List<Component> s_ComponentList = new List<Component>();
        [NoAutoStaticsCleanup] // Reusable scratch buffer, always Clear()ed before and after use; holds no live references across reload.
        static List<Component> s_AssetComponentList = new List<Component>();

        static void ThrowExceptionIfNullOrNotPartOfPrefabInstance(GameObject prefabInstance)
        {
            if (prefabInstance == null)
                throw new ArgumentNullException(nameof(prefabInstance));

            if (!PrefabUtility.IsPartOfPrefabInstance(prefabInstance))
                throw new ArgumentException("Provided GameObject is not a Prefab instance");
        }

        public static List<ObjectOverride> GetObjectOverrides(GameObject prefabInstance, bool includeDefaultOverrides = false)
        {
            ThrowExceptionIfNullOrNotPartOfPrefabInstance(prefabInstance);

            var prefabInstanceRoot = PrefabUtility.GetOutermostPrefabInstanceRoot(prefabInstance);

            // From root of instance traverse all child go and detect any GameObjects or components
            // that are not part of that source prefab objects component list (these must be added)
            TransformVisitor transformVisitor = new TransformVisitor();
            var modifiedObjects = new List<ObjectOverride>();

            Func<Transform, object, bool> checkMethod;
            if (includeDefaultOverrides)
                checkMethod = CheckForModifiedObjectsIncludingDefaultOverrides;
            else
                checkMethod = CheckForModifiedObjectsExcludingDefaultOverrides;

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Call PrefabUtility.IsPartOfPrefabInstance(go) before passing the GameObject to GetObjectOverrides
2. If the object might be a prefab asset, use PrefabUtility.IsPartOfPrefabAsset to distinguish and route accordingly
3. Validate Selection.activeGameObject or the user-provided object before processing

Example fix

// before
var overrides = PrefabOverridesUtility.GetObjectOverrides(selectedGo);

// after
if (selectedGo != null && PrefabUtility.IsPartOfPrefabInstance(selectedGo))
    var overrides = PrefabOverridesUtility.GetObjectOverrides(selectedGo);
else
    Debug.LogWarning("Selection is not a prefab instance.");

if (!PrefabUtility.IsPartOfPrefabInstance(prefabInstance))
{
    Debug.LogWarning("GameObject is not a prefab instance — overrides are not applicable.");
    return;
}
// Safe to call GetObjectOverrides(prefabInstance)

static bool IsPrefabInstance(GameObject go) => go != null && PrefabUtility.IsPartOfPrefabInstance(go);

try { var overrides = PrefabOverridesUtility.GetObjectOverrides(go); }
catch (ArgumentException ex) when (ex.Message == "Provided GameObject is not a Prefab instance")
{ Debug.LogWarning($"{go.name} is not a prefab instance."); }

When it happens

Trigger: Calling PrefabOverridesUtility.GetObjectOverrides on a plain scene GameObject, a prefab asset in the Project window, or any object that PrefabUtility.IsPartOfPrefabInstance returns false for.

Common situations: Editor tools that operate on the current selection without verifying it is a prefab instance. Code that handles both prefab assets and instances in the same path. Unpacking a prefab instance and then trying to query its overrides.

Related errors

• Given input object is not a prefab asset
• Object to create variant from has to be a Prefab root
• PersistentLocalStorageSize must be between 256 and 4096, but
• guid
• prefabInstance

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/414599afd271bf2f. Report an issue: GitHub.