> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/4100-to-4106/aur4109.md).

# AUR4109

## Error Message

`AUR4109: Invalid rule execution result.`

## Description

This error occurs when the validation system receives an invalid value from a rule execution (for example a non-boolean/non-result value).

## Common Scenarios

```ts
// ❌ Returning a string instead of a boolean/result
const badRule = () => 'yes' as any;
```

## Solution

* Ensure rule implementations return `true/false` (or the expected validation result object), or a `Promise` of that value.

## Troubleshooting

* Identify the rule that produced the invalid result and fix its return type.
* If you wrap/compose rules, ensure wrappers preserve the expected result type.


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