Control.OnExit when clicking on Help button


I have a dialog with an edit control. This edit control has an OnExit event,
which check the value of the edit control. If I click on the Help button, I
don't want the OnExit fired, the edit control must not lose the focus. I
could use a TSpeedButton, but then, when I use the Tab, the button can't
never be focused. So it's only the mouse which is the problem.

Any hints would be appreciated.