diff --git a/config/bootscripts/boot-rockchip64.cmd b/config/bootscripts/boot-rockchip64.cmd
index a2a952a5b9..3050dd92fe 100644
--- a/config/bootscripts/boot-rockchip64.cmd
+++ b/config/bootscripts/boot-rockchip64.cmd
@@ -14,7 +14,7 @@ setenv rootfstype "ext4"
 setenv docker_optimizations "on"
 setenv earlycon "off"
 
-env exists distro_bootpart || setenv distro_bootpart 1
+test -n "${distro_bootpart}" || distro_bootpart=1
 
 echo "Boot script loaded from ${devtype} ${devnum}:${distro_bootpart}"