TabbedPage binding to SelectedItem - no response

I have the following in my xaml:

<TabbedPage SelectedItem="{Binding CurrentTab}">
<Children>
    <local:HomepageView />
    <local:OtherPageView />
</Children>
</TabbedPage>

In my viewModel I've got:

private Page currentTab;

    public Page CurrentTab
    {
        get
        {
            return currentTab;
        }

        set
        {
            currentTab = value;
            OnPropertyChanged("CurrentTab");
        }
    }

However, the binding never fires! Anyone know what needs to be done to make this work?