Word wrap in RichTextBox

[hain]

I have a WPF project containing a RichTextBox. I want the text not to wrap. I can force this by setting the PageWidth for the contained FlowDocument to be a large number. However, I really want the PageWidth to adjust itself to the length of the longest line (paragraph), so that the horizontal scroll bar thumb will have an appropriate length. I tried setting PageWidth to Auto, but this did not prevent wrapping. Thanks for your suggestions! tfhain