vercel/ai · error · InvalidArgumentError

Invalid argument for parameter schema: Schema is not support

Error message

Invalid argument for parameter schema: Schema is not supported for enum output.

What it means

output: 'enum' makes the model select one value from enumValues; it does not use a schema. Passing schema (or an enum zod schema) with enum output is contradictory, so the library throws InvalidArgumentError.

Source

Thrown at packages/ai/src/generate-object/validate-object-generation-input.ts:103

      throw new InvalidArgumentError({
        parameter: 'schema',
        value: schema,
        message: 'Element schema is required for array output.',
      });
    }

    if (enumValues != null) {
      throw new InvalidArgumentError({
        parameter: 'enumValues',
        value: enumValues,
        message: 'Enum values are not supported for array output.',
      });
    }
  }

  if (output === 'enum') {
    if (schema != null) {
      throw new InvalidArgumentError({
        parameter: 'schema',
        value: schema,
        message: 'Schema is not supported for enum output.',
      });
    }

    if (schemaDescription != null) {
      throw new InvalidArgumentError({
        parameter: 'schemaDescription',
        value: schemaDescription,
        message: 'Schema description is not supported for enum output.',
      });
    }

    if (schemaName != null) {
      throw new InvalidArgumentError({
        parameter: 'schemaName',
        value: schemaName,

View on GitHub (pinned to 69428b1f8b)

Solutions

Remove the schema property and keep only enumValues with output: 'enum'.
If a schema is what you need (e.g. z.enum field inside an object), use output: 'object' instead.
Update helpers/wrappers to conditionally attach schema only for object/array output.

Example fix

// before
generateObject({ model, output: 'enum', enumValues: ['a','b'], schema: z.enum(['a','b']), prompt });
// after
generateObject({ model, output: 'enum', enumValues: ['a','b'], prompt });

Defensive patterns

Strategy: validation

Validate before calling

if (opts.output === 'enum' && opts.schema != null) {
  throw new Error("schema must be omitted when output is 'enum'; use enumValues");
}

Type guard

function isEnumOptionsValid(opts) {
  return opts.output !== 'enum' || (opts.schema == null && opts.enumValues != null);
}

Try / catch

try {
  return await generateObject(opts);
} catch (error) {
  if (InvalidArgumentError.isInstance(error) && error.parameter === 'schema' && opts.output === 'enum') {
    const { schema, ...rest } = opts;
    return generateObject(rest);
  }
  throw error;
}

Prevention

With output: 'enum', specify enumValues only; drop schema and z.enum schemas.
Use output: 'object' if you want the value embedded in a structured object.
Conditionally build options per output mode in helper functions.

When it happens

Trigger: Calling generateObject({ model, output: 'enum', enumValues: [...], schema: someSchema, prompt }) or streamObject with schema set alongside enum output; any non-null schema with output: 'enum' triggers it.

Common situations: Previously passing a z.enum(...) schema and then also adding output: 'enum'/enumValues during migration; shared helper that always attaches schema; copy-pasted object-output code changed to enum output.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/f121edd2a0cef2cb. Report an issue: GitHub.