diff --git a/conf/machine/freedom-u540.conf b/conf/machine/freedom-u540.conf
index 1f697d2..960a0a5 100644
--- a/conf/machine/freedom-u540.conf
+++ b/conf/machine/freedom-u540.conf
@@ -9,8 +9,8 @@ MACHINE_FEATURES = "screen keyboard ext2 ext3 serial"
 
 KERNEL_IMAGETYPE = "vmlinux"
 
-PREFERRED_PROVIDER_virtual/kernel = "linux-riscv"
-PREFERRED_VERSION_linux-riscv = "4.15%"
+PREFERRED_PROVIDER_virtual/kernel ?= "linux-riscv"
+PREFERRED_VERSION_linux-riscv ?= "4.15%"
 
 GDBVERSION = "riscv"
 QEMUVERSION = "riscv"
diff --git a/conf/machine/qemuriscv64.conf b/conf/machine/qemuriscv64.conf
index b2c779d..79249a2 100644
--- a/conf/machine/qemuriscv64.conf
+++ b/conf/machine/qemuriscv64.conf
@@ -2,6 +2,9 @@
 #@NAME: generic riscv64 machine
 #@DESCRIPTION: Machine configuration for running a generic riscv64
 
+PREFERRED_PROVIDER_virtual/kernel ?= "linux-riscv"
+PREFERRED_VERSION_linux-riscv ?= "4.15%"
+
 require conf/machine/include/qemu.inc
 require conf/machine/include/tune-riscv.inc
 
@@ -9,9 +12,6 @@ MACHINE_FEATURES = "screen keyboard ext2 ext3 serial"
 
 KERNEL_IMAGETYPE = "vmlinux"
 
-PREFERRED_PROVIDER_virtual/kernel = "linux-riscv"
-PREFERRED_VERSION_linux-riscv = "4.15%"
-
 GDBVERSION = "riscv"
 QEMUVERSION = "riscv"