How to implement a number maximum with a decimal step limit

Hi,

I have these two requirements:
1) I need to implement a maximum of 64.0 for a Double value
2) The double value can only have steps of "0.5"

I would prefer a behavior where the user's typing is restricted, as opposed to a post edit validation mechanism (ValidatesOnDataErrors).

I've implemented a MaskedTextBox with the following Mask: "[0-9]{0,2}[.][0,5]"
But, there appears to be no Maximum property on a MaskedTextBox.

I've also implemented a DoubleEditBox, with my maximum of 64.0, but I cannot figure out a way to implement the "0.5" increment limitation that is applied while the user types.

Is there an easy way to achieve this goal?

Thanks,
Greg