Add windows server 2008 r2 domain controller to windows 2008 domain

Hi, 

All my domain controllers are running on Windows Server 2008 servers. We are going to add one more additional domain controller in an existing forest and site. Is there a problem if install the new domain controller on a Windows Server 2008 R2 operating system? Or do I need to go with 2008 (non-R2) server for the new additional domain controller as well.

I appreciate any help in advance.

Thanks,V
Vipin