IsEnabled property problem on ToolbarItem

Hi,
I have problem with binding value of IsEnabled property on ToolbarItem.

In my ModelView I have property:
public bool IsItemSelected { get; set; }
which is set on false in constructor.

In my View I have ToolbarItems with this item:

<ToolbarItem Name="Edit" Order="Primary" Priority="1" IsEnabled="{Binding IsItemSelected}">

When I start my app, it throws XamlParseException:

Cannot assign property "IsEnabled": type mismatch between "Xamarin.Forms.Binding" and "System.Boolean"

I tried also Value Converter, but it doesn't work too.

Does anyone know how to fix it? Any other Binding works find, such as ListView or some text properties.