jaredpalmer/formik · warning

Warning: An unhandled error was caught during validation in

Error message

Warning: An unhandled error was caught during validation in <Formik validationSchema />

What it means

Formik ran your Yup `validationSchema` and Yup threw an error that is NOT a `ValidationError` (e.g. TypeError, a schema bug, or a rejected promise from a lazy/async schema). Formik maps `ValidationError` to form errors; any other exception is a real bug, so it warns (dev only) and re-throws via rejection.

Source

Thrown at packages/formik/src/Formik.tsx:256

        field && schema.validateAt
          ? schema.validateAt(field, values)
          : validateYupSchema(values, schema);
      return new Promise((resolve, reject) => {
        promise.then(
          () => {
            resolve(emptyErrors);
          },
          (err: any) => {
            // Yup will throw a validation error if validation fails. We catch those and
            // resolve them into Formik errors. We can sniff if something is a Yup error
            // by checking error.name.
            // @see https://github.com/jquense/yup#validationerrorerrors-string--arraystring-value-any-path-string
            if (err.name === 'ValidationError') {
              resolve(yupToFormErrors(err));
            } else {
              // We throw any other errors
              if (process.env.NODE_ENV !== 'production') {
                console.warn(
                  `Warning: An unhandled error was caught during validation in <Formik validationSchema />`,
                  err
                );
              }

              reject(err);
            }
          }
        );
      });
    },
    [props.validationSchema]
  );

  const runSingleFieldLevelValidation = React.useCallback(
    (field: string, value: void | string): Promise<string> => {
      return new Promise(resolve =>
        resolve(fieldRegistry.current[field].validate(value) as string)

View on GitHub (pinned to 91475adbf3)

Solutions

1. Look at the second warn argument (the raw err) — it is the actual thrown error with stack; fix that.
2. Wrap custom Yup `test()` message/test functions defensively; guard property access inside tests.
3. Verify you're on a single compatible yup version (`npm ls yup`) — mismatched versions can produce errors not shaped like ValidationError.
4. Reproduce by calling `schema.validate(values)` manually in a unit test to see the raw exception.

Example fix

// before
validationSchema: Yup.object().shape({
  email: Yup.string().test('domain', 'bad', v => v.split('@')[1] === 'x.com'), // throws on undefined
})
// after
validationSchema: Yup.object().shape({
  email: Yup.string().test('domain', 'bad', v =>
    typeof v === 'string' && v.split('@')[1] === 'x.com'
  ),
})

// sanity-check the schema in a test/dev before using it
schema.validateSync(initialValues); // surfaces non-ValidationError throws early

import * as Yup from 'yup';
const isValidSchema = (s: unknown): s is Yup.ObjectSchema =>
  !!s && typeof (s as Yup.ObjectSchema).validate === 'function';

// custom Yup tests: keep them total (never throw)
Yup.string().test('check', 'msg', v => {
  try { return check(v); } catch { return false; }
})

When it happens

Trigger: A `validationSchema` whose schema construction throws (e.g. `Yup.object().shape({ a: undefined })`), a `lazy()` schema that throws, casting/reach issues, or runtime TypeErrors inside custom Yup test functions.

Common situations: Custom `test()` callbacks that access undefined properties, mixing Yup versions where `ValidationError.name` differs, conditionally building a schema with a bug, or schema referenced before definition.

Related errors

• Warning: An unhandled error was caught during validation in
• Warning: An unhandled error was caught from submitForm()
• Warning: Formik called \`${handlerName}\`, but you forgot to

AI-assisted analysis of jaredpalmer/formik@91475adbf3 (2026-08-27). Data as JSON: /api/errors/c7fa53400aafbed4. Report an issue: GitHub.