diff -rup libvirt-0.6.3/src/xm_internal.c libvirt-0.6.3.new/src/xm_internal.c
--- libvirt-0.6.3/src/xm_internal.c	2009-06-12 11:10:10.000000000 -0400
+++ libvirt-0.6.3.new/src/xm_internal.c	2009-06-12 11:09:45.000000000 -0400
@@ -2936,6 +2936,7 @@ xenXMDomainDetachDevice(virDomainPtr dom
                             def->disks + i + 1,
                             sizeof(*def->disks) *
                             (def->ndisks - (i + 1)));
+                def->ndisks--;
                 break;
             }
         }
@@ -2954,6 +2955,7 @@ xenXMDomainDetachDevice(virDomainPtr dom
                             def->nets + i + 1,
                             sizeof(*def->nets) *
                             (def->nnets - (i + 1)));
+                def->nnets--;
                 break;
             }
         }