Angularjs disable button if checkbox is checked

I have a button on a form that I'd like to disable until one or more checkboxes have been selected. This is probably fairly simple to solve, but the button is not disabled when I use !result.isSelected.

This is my button:

<button class="btn btn-success" ng-click="send()"  ng-disabled="!result.isSelected" </button>

And the checkbox:

<input type="checkbox" class="checkbox-row" ng-model="result.isSelected" ng-click="selected()" />

Does anyone know of a better solution? Thanks for your help!