vercel/ai · error · InvalidArgumentError

Invalid argument for parameter enumValues: Enum values are n

Error message

Invalid argument for parameter enumValues: Enum values are not supported for array output.

What it means

enumValues apply only to output: 'enum'. With output: 'array' the model produces a JSON array of elements shaped by the element schema, so enumValues is invalid and InvalidArgumentError is thrown.

Source

Thrown at packages/ai/src/generate-object/validate-object-generation-input.ts:93

      throw new InvalidArgumentError({
        parameter: 'enumValues',
        value: enumValues,
        message: 'Enum values are not supported for object output.',
      });
    }
  }

  if (output === 'array') {
    if (schema == null) {
      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({

View on GitHub (pinned to 69428b1f8b)

Solutions

Remove enumValues from the array-output call.
If you need an array of enum values, use output: 'array' with schema: z.enum(['a','b']).
If you need a single enum pick, use output: 'enum' instead.

Example fix

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

Defensive patterns

Strategy: validation

Validate before calling

if (opts.output === 'array' && opts.enumValues != null) {
  throw new Error("enumValues are only valid with output: 'enum'");
}

Type guard

function isArrayOptionsWithoutEnum(opts) {
  return opts.output !== 'array' || opts.enumValues == null;
}

Try / catch

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

Prevention

For arrays of enum values use schema: z.enum([...]) with output: 'array'.
Keep enumValues out of shared option factories.
Type options per output mode so invalid combinations fail at compile time.

When it happens

Trigger: Calling generateObject({ model, output: 'array', schema, enumValues: [...] }) or streamObject with the same combination.

Common situations: Shared options object reused across enum and array calls; converting an enum-generation call to array output without removing enumValues; abstraction layers that always include enumValues.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/5c827e9cb46efb8b. Report an issue: GitHub.