mantinedev/mantine · error · Error

[@mantine/core] Duplicate options are not supported. Option…

Error message

[@mantine/core] Duplicate options are not supported. Option with value "${option.value}" was provided more than once

What it means

Combobox-based components require all option values to be unique. During render, Mantine builds a set of seen values and throws when the same value appears twice, because duplicate values make selection, keyboard navigation and label lookup ambiguous.

Solutions

1. Deduplicate the data array by value before passing it: const unique = [...new Map(data.map((o) => [o.value, o])).values()]
2. Fix the source data so each option has a distinct value
3. If values come from an API, deduplicate on fetch or fix the backend query

Example fix

// before
const data = [
  { value: 'a', label: 'One' },
  { value: 'a', label: 'Two' },
];

// after
const data = [
  { value: 'a', label: 'One' },
  { value: 'b', label: 'Two' },
];

// or dedupe programmatically
const data = [...new Map(raw.map((o) => [o.value, o])).values()];

const uniqueByValue = (data) =>
  [...new Map(data.map((o) => [o.value, o])).values()];

<Select data={uniqueByValue(rawData)} />;

function hasUniqueValues(data: { value: string }[]): boolean {
  return new Set(data.map((o) => o.value)).size === data.length;
}

When it happens

Trigger: Passing data with two options having the same value string, e.g. [{ value: 'a', label: '1' }, { value: 'a', label: '2' }]; concatenating two API result sets that share ids; grouped data where the same value appears in two different groups.

Common situations: Merging static defaults with server-fetched options that overlap; API returning duplicate records; case differences intended as distinct (values are compared as exact strings); refactoring numbers to strings causing collisions (e.g. 1 and '1' both stringified).

Related errors

• [@mantine/core] Each option must have value property
• Combobox.DropdownTarget component children should be an…
• Combobox.EventsTarget component children should be an…
• Combobox.Target component children should be an element or…

AI-assisted analysis of mantinedev/mantine@8a284e2c2c (2026-08-28). Data as JSON: /api/errors/0986cf63f275f009. Report an issue: GitHub.

Appendix: source

Thrown at packages/@mantine/core/src/components/Combobox/OptionsDropdown/validate-options.ts:17

import { isOptionsGroup } from './is-options-group';

export function validateOptions(options: any[], valuesSet = new Set()) {
  if (!Array.isArray(options)) {
    return;
  }

  for (const option of options) {
    if (isOptionsGroup(option)) {
      validateOptions(option.items, valuesSet);
    } else {
      if (typeof option.value === 'undefined') {
        throw new Error('[@mantine/core] Each option must have value property');
      }

      if (valuesSet.has(option.value)) {
        throw new Error(
          `[@mantine/core] Duplicate options are not supported. Option with value "${option.value}" was provided more than once`
        );
      }

      valuesSet.add(option.value);
    }
  }
}

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