[CentOS-virt] Time lagging on DomU

Hi, on one of our systems I see that while the time on the Centos 5.4 Host is correct it lags behind on two of the 5.5 guests by almost 5 minutes but is correct for the third domU. From what I understand the clock of the system is controlled by the host and and guest cannot write to it (and because of that not change it). Does anyone now what the cause could be and how I can fix the time for the guests?

Running kernel versions: Host (correct time): 2.6.18-164.15.1.el5xen guest 1 (correct time): 2.6.18-194.3.1.el5xen guest 2 (wrong time): 2.6.18-194.32.1.el5xen guest 3 (wrong time): 2.6.18-194.el5xen

Regards, Dennis