diff --git a/Makefile b/Makefile
index 64b7327..5edce42 100644
--- a/Makefile
+++ b/Makefile
@@ -66,7 +66,7 @@ raspi_4_buster.yaml: raspi_base_buster.yaml
 	cat raspi_base_buster.yaml | sed "s/__ARCH__/arm64/" | \
 	sed "s#raspi3-firmware#raspi-firmware/buster-backports#" | \
 	sed "s#apt-get update#echo 'APT::Default-Release \"buster\";' > /etc/apt/apt.conf\n      apt-get update#" | \
-	sed "s#\(RASPIROOT.*cmdline.txt\)#\1\n      sed -i 's/cma=64M //' /boot/firmware/cmdline.txt\n      sed -i 's/cma=\\\$$CMA //' /etc/kernel/postinst.d/z50-raspi-firmware#" | \
+	sed "s#\(RASPIROOT.*cmdline.txt\)#\1\n      sed -i 's/cma=64M //' /boot/firmware/cmdline.txt#" | \
 	sed "s/__LINUX_IMAGE__/linux-image-arm64\/buster-backports/" | \
 	sed "s/__EXTRA_PKGS__/- firmware-brcm80211\/buster-backports/" | \
 	sed "s/__DTB__/\\/usr\\/lib\\/linux-image-*-arm64\\/broadcom\\/bcm*rpi*.dtb/" |\
@@ -113,7 +113,7 @@ raspi_3_bullseye.yaml: raspi_base_bullseye.yaml
 
 raspi_4_bullseye.yaml: raspi_base_bullseye.yaml
 	cat raspi_base_bullseye.yaml | sed "s/__ARCH__/arm64/" | \
-	sed "s#\(RASPIROOT.*cmdline.txt\)#\1\n      sed -i 's/cma=64M //' /boot/firmware/cmdline.txt\n      sed -i 's/cma=\\\$$CMA //' /etc/kernel/postinst.d/z50-raspi-firmware#" | \
+	sed "s#\(RASPIROOT.*cmdline.txt\)#\1\n      sed -i 's/cma=64M //' /boot/firmware/cmdline.txt#" | \
 	sed "s/__LINUX_IMAGE__/linux-image-arm64/" | \
 	sed "s/__EXTRA_PKGS__/- firmware-brcm80211/" | \
 	sed "s/__DTB__/\\/usr\\/lib\\/linux-image-*-arm64\\/broadcom\\/bcm*rpi*.dtb/" |\
diff --git a/raspi_master.yaml b/raspi_master.yaml
index 9a8cb3f..5289525 100644
--- a/raspi_master.yaml
+++ b/raspi_master.yaml
@@ -137,14 +137,17 @@ steps:
       rm -rf /var/lib/apt/lists
 
   # Modify the kernel commandline we take from the firmware to boot from
-  # the partition labeled raspiroot instead of forcing it to mmcblk0p2
+  # the partition labeled raspiroot instead of forcing it to mmcblk0p2.
+  # Also insert the serial console right before the root= parameter.
   #
   # These changes will be overwritten after the hardware is probed
-  # after dpkg reconfigures raspi-firmware (upon first boot).
+  # after dpkg reconfigures raspi-firmware (upon first boot), so make
+  # sure we don't lose label-based booting.
   - chroot: /
     shell: |
-      sed -i 's/^/console=__SERIAL_CONSOLE__ /' /boot/firmware/cmdline.txt
-      sed -i 's/.dev.mmcblk0p2/LABEL=RASPIROOT/' /boot/firmware/cmdline.txt
+      sed -i 's/root=/console=__SERIAL_CONSOLE__ root=/' /boot/firmware/cmdline.txt
+      sed -i 's#root=/dev/mmcblk0p2#root=LABEL=RASPIROOT#' /boot/firmware/cmdline.txt
+      sed -i 's/^#ROOTPART=.*/ROOTPART=LABEL=RASPIROOT/' /etc/default/raspi-firmware
 
   # TODO(https://github.com/larswirzenius/vmdb2/issues/24): remove once vmdb
   # clears /etc/resolv.conf on its own.