diff --git a/target/linux/ath79/mikrotik/base-files/lib/upgrade/platform.sh b/target/linux/ath79/mikrotik/base-files/lib/upgrade/platform.sh
index 5ee54923698..97d388168f5 100644
--- a/target/linux/ath79/mikrotik/base-files/lib/upgrade/platform.sh
+++ b/target/linux/ath79/mikrotik/base-files/lib/upgrade/platform.sh
@@ -39,7 +39,7 @@ platform_do_upgrade() {
 		;;
 	*)
 		# NOR devices: erase firmware if booted from initramfs
-		[ -z "$(rootfs_type)" ] && mtd erase firmware
+		[ "$(rootfs_type)" = "tmpfs" ] && mtd erase firmware
 
 		default_do_upgrade "$1"
 		;;
diff --git a/target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh b/target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh
index c68b012d0b6..99ed36e4291 100755
--- a/target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh
+++ b/target/linux/ramips/mt7621/base-files/lib/upgrade/platform.sh
@@ -31,7 +31,7 @@ platform_do_upgrade() {
 	mikrotik,routerboard-760igs|\
 	mikrotik,routerboard-m11g|\
 	mikrotik,routerboard-m33g)
-		[ -z "$(rootfs_type)" ] && mtd erase firmware
+		[ "$(rootfs_type)" = "tmpfs" ] && mtd erase firmware
 		;;
 	asus,rt-ac65p|\
 	asus,rt-ac85p)