how to make sure page validates prior to disabling the button

<asp:Button runat="server" ID="BtnSubmit"
OnClientClick="this.disabled = true; this.value = 'Submitting...';"
UseSubmitBehavior="false"
OnClick="BtnSubmit_Click"
Text="Submit Me!" />
 I am disabling my submit button once the user clicks it to avoid multiple submits. There is one gotcha tough and that is if one of the validator controls fires the button stays disabled how can I avoid this. How can I make sure validation takes place and the page validates prior to disabling the button.
I am using if (Page.IsValid)
...