diff --git a/debian/changelog b/debian/changelog
index 16b8d012..c600af97 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,13 @@
+livecd-rootfs (2.408.39) UNRELEASED; urgency=medium
+
+  * Backport support for building ubuntu-core images with ubuntu-image (using
+    IMAGEFORMAT=ubuntu-image).
+  * Decide what model assertion series to fetch depending on the suite. Use 16
+    for xenial and 18 for other series (bionic+). This enables core18 image
+    builds (LP: #1799736).
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Thu, 04 Oct 2018 19:30:17 +0200
+
 livecd-rootfs (2.408.38) xenial; urgency=medium
 
   * ubuntu-cpc: Handle a pre-existing /lib/modules in 030-root-tarball.hook
diff --git a/debian/control b/debian/control
index ab1cc33f..00739806 100644
--- a/debian/control
+++ b/debian/control
@@ -30,7 +30,9 @@ Depends: ${misc:Depends},
          python3-software-properties,
          qemu-utils,
          rsync,
+         snapd,
          squashfs-tools (>= 1:3.3-1),
+         ubuntu-image,
          vmdk-stream-converter [amd64 i386],
          xz-utils,
          zerofree
diff --git a/live-build/auto/build b/live-build/auto/build
index 69d8d94d..24a68ad5 100755
--- a/live-build/auto/build
+++ b/live-build/auto/build
@@ -10,6 +10,28 @@ Arguments "${@}"
 Read_conffiles config/all config/common config/bootstrap config/chroot config/binary config/source
 Set_defaults
 
+if [ -z "${PROJECT:-}" ]; then
+    echo "PROJECT environment variable has to be set" >&2
+    exit 1
+fi
+
+. config/functions
+
+# Link output files somewhere BuildLiveCD will be able to find them.
+PREFIX="livecd.$PROJECT${SUBARCH:+-$SUBARCH}"
+
+if [ "${IMAGEFORMAT:-}" = "ubuntu-image" ]; then
+	# Use ubuntu-image instead of live-build
+
+	CHANNEL="${CHANNEL:-edge}"
+	env SNAPPY_STORE_NO_CDN=1 \
+	ubuntu-image -c "$CHANNEL" $UBUNTU_IMAGE_ARGS \
+		-o "$PREFIX".img "$PREFIX".model-assertion
+	xz -0 -T4 "$PREFIX".img
+	mv seed.manifest "$PREFIX".manifest
+	exit 0
+fi
+
 # Setup cleanup function
 Setup_cleanup
 
@@ -350,9 +372,6 @@ else
 	exit 1
 fi
 
-# Link output files somewhere BuildLiveCD will be able to find them.
-PREFIX="livecd.$PROJECT${SUBARCH:+-$SUBARCH}"
-
 case $LB_INITRAMFS in
 	casper)
 		INITFS="casper"
diff --git a/live-build/auto/config b/live-build/auto/config
index 2e7c2e25..9eef13e9 100755
--- a/live-build/auto/config
+++ b/live-build/auto/config
@@ -96,6 +96,7 @@ LIVE_TASK=
 PREINSTALLED=false
 PREINSTALL_POOL=
 PREINSTALL_POOL_SEEDS=
+PREFIX="livecd.$PROJECT${SUBARCH:+-$SUBARCH}"
 
 CHROOT_HOOKS=
 BINARY_HOOKS=
@@ -144,6 +145,53 @@ case $IMAGEFORMAT in
 		PREINSTALLED=true
 		;;
 
+	ubuntu-image)
+		case "$ARCH+${SUBARCH:-}" in
+			amd64+*)
+				MODEL=pc-amd64 ;;
+			i386+*)
+				MODEL=pc-i386 ;;
+			arm64+snapdragon)
+				MODEL=dragonboard ;;
+			armhf+raspi2)
+				MODEL=pi2 ;;
+			armhf+raspi3)
+				MODEL=pi3 ;;
+			armhf+cm3)
+				MODEL=cm3 ;;
+			*)
+				echo "Model $ARCH+${SUBARCH:-} unknown to livecd-rootfs" >&2
+				exit 1
+				;;
+		esac
+		case $MODEL in
+			pc-amd64|pc-i386)
+				UBUNTU_IMAGE_ARGS="--image-size 3700M" ;;
+			*)
+				UBUNTU_IMAGE_ARGS="" ;;
+		esac
+		case $SUITE in
+			xenial)
+				# Ubuntu Core 16
+				;;
+			*)
+				# Ubuntu Core 18
+				MODEL="ubuntu-core-18-${MODEL#pc-}" ;;
+		esac
+
+		echo "IMAGEFORMAT=$IMAGEFORMAT" >> config/common
+		echo "UBUNTU_IMAGE_ARGS=\"$UBUNTU_IMAGE_ARGS\"" >> config/common
+		# Store model assertion in top dir to get it picked up later as a build artifact
+		env SNAPPY_STORE_NO_CDN=1 snap known --remote model series=16 model="$MODEL" brand-id=canonical > "$PREFIX".model-assertion
+		echo "Configured ubuntu-image for the following model assertion:"
+		cat "$PREFIX".model-assertion
+		echo "----------------------------------------------------------"
+		# Fake finished configuration for lb build
+		mkdir -p .build
+		touch .build/config
+		exit 0
+		;;
+
 	none)
 		OPTS="${OPTS:+$OPTS }--chroot-filesystem $IMAGEFORMAT"
 		;;