The “listbox” role is not allowed for element “select” without a “multiple” attribute and without a “size” attribute whose value is greater than 1.

The listbox role is the implicit ARIA role for a <select> element only when it has a multiple attribute or a size attribute greater than 1. A standard single-selection <select> (dropdown) has an implicit role of combobox, so explicitly assigning role="listbox" to it creates a conflict.

When a <select> element has no multiple attribute and no size greater than 1, browsers render it as a collapsed dropdown — a combobox. The listbox role describes a widget where all options are persistently visible, which matches the behavior of a multi-select or a select with a visible size greater than 1. Applying role="listbox" to a standard dropdown misrepresents the control to assistive technologies.

You have a few options to fix this: remove the role="listbox" entirely (since the browser already assigns the correct implicit role), add the multiple attribute, or set size to a value greater than 1.

Incorrect Example

<select role="listbox" name="color">
  <option value="red">Red</option>
  <option value="blue">Blue</option>
  <option value="green">Green</option>
</select>

Fixed Examples

Remove the explicit role and let the browser handle it:

<select name="color">
  <option value="red">Red</option>
  <option value="blue">Blue</option>
  <option value="green">Green</option>
</select>

Or, if you genuinely need role="listbox", use multiple or size greater than 1:

<select role="listbox" name="color" multiple>
  <option value="red">Red</option>
  <option value="blue">Blue</option>
  <option value="green">Green</option>
</select>

<select role="listbox" name="color" size="3">
  <option value="red">Red</option>
  <option value="blue">Blue</option>
  <option value="green">Green</option>
</select>

In most cases, simply removing role="listbox" is the best fix. The implicit ARIA roles already convey the correct semantics to assistive technologies without any extra attributes.

Learn more:

MDN Reference

Using ARIA: role=listbox

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MDN Reference

HTML select element

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W3C Reference

ARIA in HTML specification

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