diff --git a/conf/machine/nitrogen6x.conf b/conf/machine/nitrogen6x.conf
index f9b6cab..f35460d 100644
--- a/conf/machine/nitrogen6x.conf
+++ b/conf/machine/nitrogen6x.conf
@@ -43,7 +43,7 @@ KERNEL_DEVICETREE = "imx6q-sabrelite.dtb \
 KERNEL_IMAGETYPE = "zImage"
 
 PREFERRED_PROVIDER_u-boot = "u-boot-boundary"
-PREFERRED_PROVIDER_virtual/kernel ?= "linux-boundary"
+PREFERRED_PROVIDER_virtual/kernel ??= "linux-boundary"
 
 # Use SPI NOR U-Boot by default
 IMAGE_BOOTLOADER ?= ""