# AUR0109

## Error Message

`AUR0109: Ast eval error: unknown unary operator: "{{op}}"`

## Description

This error occurs when Aurelia encounters a unary operator it does not support while evaluating an expression.

## Solution

* Use supported operators, or move complex logic into a view-model method.

## More Information

This code is also documented under the runtime-html section: [AUR0109](https://docs.aurelia.io/developer-guides/error-messages/runtime-html/aur0109).