How to prevent modifying the same sales order in R/3 & CRM at the same time

Guys,

We are using CRM 5.0& R/3 4.6C. We have the middle set up. I have noticed that its possible to open the same sales order in R/3 and CRM in the change mode. I believe this could cause inconsistenices if the users modify the same order in different systems. Is there a standar way to prevent this from happening.

Is there something like a change lock like we have the distribution lock?

Anirudh