Unity-Technologies/UnityCsReference · error · ArgumentException

Specified enumType must be System.Enum

Error message

Specified enumType must be System.Enum

What it means

Thrown by the int-flag overload of EnumFlagsField when enumType.IsEnum is false. Unlike 184, this overload legitimately accepts an int value plus a Type, so the guard is the primary defense: callers supply a Type, and if it is not an enum the method refuses. The message correctly names 'enumType'.

Solutions

1. Guard with if (!type.IsEnum) before calling the int overload.
2. Switch to the Enum-typed overload so the Type is always derived from a real enum value.
3. Fix the registry/config to reference the actual enum type, not its underlying type.

Example fix

// before
EnumFlagsField(rect, label, flags, typeof(int), false, style);

// after
EnumFlagsField(rect, label, flags, typeof(MyFlagsEnum), false, style);

if (enumType == null || !enumType.IsEnum) { Debug.LogError($"{enumType} is not an enum"); return enumValue; }

static bool IsEnumType(Type t) => t != null && t.IsEnum;

When it happens

Trigger: Calling EnumFlagsField(rect, label, someInt, someType, ...) where someType is typeof(int), typeof(string), or any non-enum. This is the realistic hit because the int overload is explicitly Type-driven.

Common situations: Generic bitfield editor utilities that store flags as int and pass a Type from a runtime registry; migrated code where the Type argument was left as the underlying integral type.

Related errors

• Parameter enumValue must be of type System.Enum
• Parameter selected must be of type System.Enum
• Unsupported enum base type for
• must be a valid
• Specify exactly one edge

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/529af9b89e57aa5a. Report an issue: GitHub.

Appendix: source

Thrown at Editor/Mono/EditorGUI.cs:4686

                throw new NotSupportedException(string.Format("Unsupported enum base type for {0}", enumType.Name));

            var id = GUIUtility.GetControlID(s_EnumFlagsField, FocusType.Keyboard, position);
            position = PrefixLabel(position, id, label);

            var flagsInt = EnumDataUtility.EnumFlagsToInt(enumData, enumValue);

            BeginChangeCheck();
            flagsInt = MaskFieldGUI.DoMaskField(position, id, flagsInt, enumData.displayNames, enumData.flagValues, style, out changedFlags, out changedToValue);
            if (!EndChangeCheck())
                return enumValue;

            return EnumDataUtility.IntToEnumFlags(enumType, flagsInt);
        }

        internal static int EnumFlagsField(Rect position, GUIContent label, int enumValue, Type enumType, bool includeObsolete, GUIStyle style)
        {
            if (!enumType.IsEnum)
                throw new ArgumentException("Specified enumType must be System.Enum", nameof(enumType));

            var enumData = EnumDataUtility.GetCachedEnumData(enumType, !includeObsolete);
            if (!enumData.serializable)
                // this is the same message used in SerializedPropertyEnumHelper.cpp
                throw new NotSupportedException(string.Format("Unsupported enum base type for {0}", enumType.Name));

            var id = GUIUtility.GetControlID(s_EnumFlagsField, FocusType.Keyboard, position);
            position = PrefixLabel(position, id, label);

            int changedFlags;
            bool changedToValue;
            return MaskFieldGUI.DoMaskField(position, id, enumValue, enumData.displayNames, enumData.flagValues, style, out changedFlags, out changedToValue, enumType.GetEnumUnderlyingType());
        }

        public static void ObjectField(Rect position, SerializedProperty property)
        {
            ObjectField(position, property, null, null, EditorStyles.objectField);
        }

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