diff --git a/meta-yocto/conf/machine/mpc8315e-rdb.conf b/meta-yocto/conf/machine/mpc8315e-rdb.conf
index 172deec68e..b30c8afef5 100644
--- a/meta-yocto/conf/machine/mpc8315e-rdb.conf
+++ b/meta-yocto/conf/machine/mpc8315e-rdb.conf
@@ -11,7 +11,7 @@ SERIAL_CONSOLE = "115200 ttyS0"
 
 MACHINE_FEATURES = "kernel26 keyboard pci ext2 ext3 serial"
 
-PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
+PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
 #PREFERRED_PROVIDER_linux-libc-headers ?= "linux-libc-headers-yocto"
 PREFERRED_PROVIDER_virtual/xserver = "xserver-kdrive"
 XSERVER = "xserver-kdrive-fbdev"
diff --git a/meta-yocto/conf/machine/routerstationpro.conf b/meta-yocto/conf/machine/routerstationpro.conf
index e6f89d848c..a0afd5d16a 100644
--- a/meta-yocto/conf/machine/routerstationpro.conf
+++ b/meta-yocto/conf/machine/routerstationpro.conf
@@ -10,7 +10,7 @@ MACHINE_FEATURES = "kernel26 screen keyboard pci usbhost ext2 ext3 \
 KERNEL_IMAGETYPE = "vmlinux"
 KERNEL_ALT_IMAGETYPE = "vmlinux.bin"
 
-PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
+PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
 #PREFERRED_PROVIDER_linux-libc-headers ?= "linux-libc-headers-yocto"
 PREFERRED_PROVIDER_virtual/xserver = "xserver-kdrive"
 XSERVER = "xserver-kdrive-fbdev"