diff --git a/live-build/ubuntu-cpc/functions b/live-build/ubuntu-cpc/functions
index 576c1a2e..6b2d69a0 100644
--- a/live-build/ubuntu-cpc/functions
+++ b/live-build/ubuntu-cpc/functions
@@ -249,4 +249,11 @@ convert_to_qcow2() {
     qemu-img info "$destination"
 }
 
+replace_grub_root_with_label() {
+    # When update-grub is run, it will detect the disks in the build system.
+    # Instead, we want grub to use the cloudimg-rootfs labelled disk
+    CHROOT_ROOT="$1"
 
+    sed -i -e "s,root=[^ ]\+,root=LABEL=cloudimg-rootfs," \
+        "$CHROOT_ROOT/boot/grub/grub.cfg"
+}
diff --git a/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary b/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary
index bcce19d7..04a3c7df 100755
--- a/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary
+++ b/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary
@@ -105,7 +105,7 @@ EOF
 
     chroot mountpoint dpkg-divert --local --rename /etc/grub.d/30_os-prober
     chroot mountpoint update-grub
-    sed -i "s,root=.* ,root=LABEL=cloudimg-rootfs ,g" mountpoint/boot/grub/grub.cfg
+    replace_grub_root_with_label mountpoint
     chroot mountpoint dpkg-divert --remove --local --rename /etc/grub.d/30_os-prober
 
     chroot mountpoint apt-get -y clean
diff --git a/live-build/ubuntu-cpc/hooks/034-disk-image-ppc64el.binary b/live-build/ubuntu-cpc/hooks/034-disk-image-ppc64el.binary
index d8c6cd3a..1f6b35a7 100755
--- a/live-build/ubuntu-cpc/hooks/034-disk-image-ppc64el.binary
+++ b/live-build/ubuntu-cpc/hooks/034-disk-image-ppc64el.binary
@@ -52,7 +52,7 @@ EOF
 
     chroot mountpoint dpkg-divert --local --rename /etc/grub.d/30_os-prober
     chroot mountpoint update-grub
-    sed -i "s,root=.* ,root=LABEL=cloudimg-rootfs ,g" mountpoint/boot/grub/grub.cfg
+    replace_grub_root_with_label mountpoint
     chroot mountpoint dpkg-divert --remove --local --rename /etc/grub.d/30_os-prober
 
     umount_partition mountpoint