Unity-Technologies/UnityCsReference · error · ArgumentException

Input GameObject is using the HideFlags.DontSaveInEditor fla

Error message

Input GameObject is using the HideFlags.DontSaveInEditor flag which is not supported when converting to Prefab instance: GameObject: 

What it means

Thrown by ThrowIfInvalidArgumentsForConvertToPrefabInstance when plainGameObject.hideFlags or its transform's hideFlags includes HideFlags.DontSaveInEditor. Objects flagged DontSaveInEditor are intentionally excluded from serialization, so converting them to a Prefab instance would produce inconsistent state. Unity rejects them before performing the conversion.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:2368

            if (IsPartOfNonAssetPrefabInstance(plainGameObject))
                throw new InvalidOperationException(string.Format("Input '{0}' is not a plain GameObject, it is already a Prefab instance. Use ReplacePrefabAssetOfPrefabInstance() instead.", plainGameObject.name));

            if (EditorUtility.IsPersistent(plainGameObject))
                throw new ArgumentException("Input is from a Prefab asset, this is not supported. Input GameObject: " + plainGameObject.name, nameof(plainGameObject));

            if (checkValidAsset)
                ThrowIfInvalidAssetForReplacePrefabInstance(prefabAssetRoot, mode);

            if (plainGameObject.transform.GetType() != prefabAssetRoot.transform.GetType())
                throw new InvalidOperationException(string.Format("Cannot convert the GameObject '{0}' with root transform of type {1} with a Prefab asset with root transform of type {2}. Transform types must match.", plainGameObject.name, plainGameObject.transform.GetType().Name, prefabAssetRoot.transform.GetType().Name));

            // Prefab Mode and EditPrefabContents scope handling
            if (PrefabStageUtility.IsGameObjectThePrefabRootInAnyPrefabStage(plainGameObject) || (EditorSceneManager.IsPreviewSceneObject(plainGameObject) && plainGameObject.transform.parent == null))
                throw new InvalidOperationException("Replacing the root GameObject in a Prefab with a Prefab instance is not supported since it will break all overrides for existing instances of this Prefab, including their positions and rotations." + plainGameObject.name);

            if (plainGameObject.hideFlags.HasFlag(HideFlags.DontSaveInEditor) || plainGameObject.transform.hideFlags.HasFlag(HideFlags.DontSaveInEditor))
                throw new ArgumentException("Input GameObject is using the HideFlags.DontSaveInEditor flag which is not supported when converting to Prefab instance: GameObject: " + plainGameObject.name, nameof(plainGameObject));

            if (mode == InteractionMode.UserAction)
            {
                // Recording undo does not handle missing scripts
                var gameObjectsWithInvalidScript = FindGameObjectsWithInvalidComponent(plainGameObject);
                if (gameObjectsWithInvalidScript.Count > 0)
                    throw new InvalidOperationException(string.Format($"Cannot convert the GameObject when it has a missing script. GameObject '{gameObjectsWithInvalidScript[0].name}' has a missing script. This is not supported by the Undo system. Use InteractionMode.AutomatedAction instead."));
            }
        }

        public static void ConvertToPrefabInstance(GameObject plainGameObject, GameObject prefabAssetRoot, ConvertToPrefabInstanceSettings settings, InteractionMode mode)
        {
            ThrowIfInvalidArgumentsForConvertToPrefabInstance(plainGameObject, prefabAssetRoot, true, mode);

            ConvertToPrefabInstance_NoInputValidation(plainGameObject, prefabAssetRoot, settings, mode);

            EditorUtility.ForceRebuildInspectors();
        }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Clear the DontSaveInEditor flag before converting: plainGameObject.hideFlags = HideFlags.None.
2. Operate on a normal serialized scene GameObject instead.
3. Guard: if (obj.hideFlags.HasFlag(HideFlags.DontSaveInEditor)) return;

Example fix

// before
PrefabUtility.ConvertToPrefabInstance(myGo, prefabAsset, settings, mode);
// myGo has HideFlags.DontSaveInEditor

// after
myGo.hideFlags = HideFlags.None;
myGo.transform.hideFlags = HideFlags.None;
PrefabUtility.ConvertToPrefabInstance(myGo, prefabAsset, settings, mode);

if (plainGameObject.hideFlags.HasFlag(HideFlags.DontSaveInEditor)
    || plainGameObject.transform.hideFlags.HasFlag(HideFlags.DontSaveInEditor))
{
    plainGameObject.hideFlags = HideFlags.None;
    plainGameObject.transform.hideFlags = HideFlags.None;
}
PrefabUtility.ConvertToPrefabInstance(plainGameObject, prefabAssetRoot, settings, mode);

static bool HasNoDontSaveFlag(GameObject obj)
{
    return obj != null
        && !obj.hideFlags.HasFlag(HideFlags.DontSaveInEditor)
        && !obj.transform.hideFlags.HasFlag(HideFlags.DontSaveInEditor);
}

When it happens

Trigger: Converting an editor-only transient GameObject (created with HideFlags.DontSaveInEditor) that was never meant to be saved. Custom preview/gizmo objects that are accidentally targeted by a conversion script.

Common situations: Editor extensions that create helper objects with DontSaveInEditor. Objects left behind by deleted tools that still carry the flag.

Related errors

• Input instance root is using the HideFlags.DontSaveInEditor
• Input '{0}' is not a Prefab instance, for plain GameObjects
• Input instance is not an outermost Prefab instance root. Inp
• Input instance root is from a Prefab asset, this is not supp
• Replacing the root Prefab instance in a Variant is not suppo

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/b6c45eda7a5b3b25. Report an issue: GitHub.