hi, it seems there should happened something with centos build system between kernel 2.6.28-128.1.1 and 2.6.18-128.1.6 compilation. because although the two spec files only differs with a few dozen of patches the resulted src.rpm are different ie: ----------------------------------------- # rpm -qp --requires kernel-2.6.18-128.1.1.el5.src.rpm | grep unifdef unifdef # rpm -qp --requires kernel-2.6.18-128.1.6.el5.src.rpm | grep unifdef # ----------------------------------------- and this small differences means the latest kernel can't be compiled in mock. what's more the same is not true for rhel's kernel ie. in case of rhel's 2.6.18-128.1.6 it gives unifdef. so it's a centos bug and with this bug centos don't follow upstream behavior. just my 2c.