diff --git a/scripts/bee-mxqsub b/scripts/bee-mxqsub
index a1c28212e..52ad7b34a 100755
--- a/scripts/bee-mxqsub
+++ b/scripts/bee-mxqsub
@@ -22,6 +22,12 @@
 # a single bee-file, where there is nothing to chain, so that the usual
 # one-package build is unchanged.
 #
+# Packages that are already built need not be part of the chain: --preinstall
+# installs their archives into the overlay before the first bee-file is built,
+# so that rebuilding, say, mesa against a released LLVM newer than the host's
+# does not rebuild LLVM as well. A pre-installed package turns the overlay on
+# even for a single bee-file.
+#
 # Note that the build tree lives in --bee-tmpdir, which defaults to the RAM
 # disk /dev/shm, so --memory has to cover the sources, the objects and the
 # build root, not just the compilers. The overlay lives there too, and holds a
@@ -72,6 +78,8 @@ staged_in=
 overlay=auto
 overlay_root=
 keep_overlay=0
+# Where --preinstall looks up a package given as name-version-revision.
+preinstall_from=/src/mariux/beeroot/packages
 keep_going=0
 dry_run=0
 run_job=0
@@ -79,6 +87,9 @@ declare -a beesh_args=()
 declare -a job_env=()
 declare -a overlay_dirs=()
 declare -a beefiles=()
+# Package archives to install into the overlay before the first build. The
+# submit phase resolves them to absolute paths, which the job phase is given.
+declare -a preinstalls=()
 # Parallel to beefiles: the bee-file each entry was copied from, for the log.
 declare -a staged_from=()
 
@@ -124,6 +135,14 @@ Options:
       --overlay-dir DIR   host directory to overlay, may be repeated
                           (default: /usr /etc)
       --keep-overlay      do not remove the overlay when the job is done
+  -p, --preinstall PKG    install the already built package PKG into the
+                          overlay before the first bee-file is built, may be
+                          repeated; PKG is a package archive or
+                          name-version-revision[.arch], looked up in the
+                          --preinstall-from directory; turns on --overlay
+      --preinstall-from DIR
+                          where to look up --preinstall packages
+                          (default: ${preinstall_from})
   -k, --keep-going        build the remaining bee-files after a failure
   -B, --beesh-arg ARG     pass ARG to beesh, may be repeated (default: -c)
   -E, --env VAR=VALUE     set VAR in the job environment, may be repeated
@@ -133,6 +152,7 @@ Options:
 Examples:
   scripts/bee-mxqsub -m 956G -t 90m -j 256 libreoffice.be0
   scripts/bee-mxqsub -t 8h SPIRV-Headers.be0 SPIRV-Tools.be0 glslang.be0 mesa.be0
+  scripts/bee-mxqsub -p llvm-23.1.3-0 -p spirv-llvm-translator-23.1.2-0 mesalib.be0
 EOF
 }
 
@@ -176,6 +196,8 @@ while (( $# )); do
 		--overlay-root)        overlay_root=$2;       shift 2 ;;
 		--overlay-dir)         overlay_dirs+=("$2");  shift 2 ;;
 		--keep-overlay)        keep_overlay=1;        shift ;;
+		-p|--preinstall)       preinstalls+=("$2");   shift 2 ;;
+		--preinstall-from)     preinstall_from=$2;    shift 2 ;;
 		-k|--keep-going)       keep_going=1;          shift ;;
 		-B|--beesh-arg)        beesh_args+=("$2");    shift 2 ;;
 		-E|--env)              job_env+=("$2");       shift 2 ;;
@@ -208,7 +230,14 @@ label=${pkg}
 (( ${#beefiles[@]} > 1 )) && label=${pkg}+$(( ${#beefiles[@]} - 1 ))
 
 if [ "${overlay}" = auto ]; then
-	if (( ${#beefiles[@]} > 1 )); then overlay=1; else overlay=0; fi
+	if (( ${#beefiles[@]} > 1 || ${#preinstalls[@]} )); then
+		overlay=1
+	else
+		overlay=0
+	fi
+fi
+if (( ${#preinstalls[@]} )) && ! (( overlay )); then
+	die "--preinstall needs the overlay, it cannot go with --no-overlay"
 fi
 
 (( ${#beesh_args[@]} )) || beesh_args=(-c)
@@ -366,6 +395,7 @@ teardown_overlay() {
 # would be lost when it exits.
 install_into_overlay() {
 	local beefile=$1 fullpkg
+	local -a archives
 
 	# beeversion reads the '# BEE_VERSION' line, so the version comes from the
 	# recipe rather than from the file name.
@@ -373,27 +403,67 @@ install_into_overlay() {
 	[ -n "${fullpkg}" ] \
 		|| { echo "cannot read the version of ${beefile##*/}" >&2; return 1; }
 
+	archives=( "${pkgdir}/${fullpkg}".*.bee.tar.bz2 )
+	if [ ! -e "${archives[0]}" ]; then
+		echo "no package archive ${pkgdir}/${fullpkg}.*.bee.tar.bz2" >&2
+		return 1
+	fi
+	if [ ${#archives[@]} -ne 1 ]; then
+		echo "several archives match ${fullpkg}: ${archives[*]}" >&2
+		return 1
+	fi
+	install_archive_into_overlay "${archives[0]}"
+}
+
+# Install the package archive ${1} into the overlay, see install_into_overlay().
+install_archive_into_overlay() {
+	local archive=$1
+
+	# Given anything but an existing file, bee would look the word up as a
+	# package name in the repository and might install something else.
+	[ -f "${archive}" ] \
+		|| { echo "package archive ${archive} not found" >&2; return 1; }
+
 	"${sandbox[@]}" bash -c '
 		set -u
-		pkgdir=$1 fullpkg=$2
-		archives=( "${pkgdir}/${fullpkg}".*.bee.tar.bz2 )
-		if [ ! -e "${archives[0]}" ]; then
-			echo "no package archive ${pkgdir}/${fullpkg}.*.bee.tar.bz2" >&2
-			exit 1
-		fi
-		if [ ${#archives[@]} -ne 1 ]; then
-			echo "several archives match ${fullpkg}: ${archives[*]}" >&2
-			exit 1
-		fi
-		allpkg=$(beeversion --format="%A" "${archives[0]}")
-		bee update --force --remove-all "${archives[0]}" || exit 1
+		archive=$1
+		allpkg=$(beeversion --format="%A" "${archive}")
+		bee update --force --remove-all "${archive}" || exit 1
 		# bee-install exits 0 even where it refuses to install and only says so
 		# on stderr, so ask whether the package really arrived.
 		if ! bee list --installed --exact "${allpkg}" | grep -q .; then
 			echo "installing ${allpkg} into the overlay failed" >&2
 			exit 1
 		fi
-	' bee-mxqsub-install "${pkgdir}" "${fullpkg}"
+	' bee-mxqsub-install "${archive}"
+}
+
+# Echo the package archive --preinstall ${1} means: the file itself if it is
+# one, else the single archive in ${preinstall_from} whose name-version-revision
+# or name-version-revision.arch is ${1}. A prefix is not enough, so that
+# llvm-23.1 does not quietly pick llvm-23.1.3-0.
+resolve_preinstall() {
+	local spec=$1 candidate
+	local -a matches=()
+
+	if [ -f "${spec}" ]; then
+		readlink -f "${spec}"
+		return 0
+	fi
+	[[ ${spec} != */* ]] || die "package archive '${spec}' not found"
+
+	for candidate in "${preinstall_from}/${spec}"*.bee.tar.bz2; do
+		[ -f "${candidate}" ] || continue
+		case ${spec} in
+			"$(beeversion --format=%F "${candidate}")"|"$(beeversion --format=%A "${candidate}")")
+				matches+=("${candidate}") ;;
+		esac
+	done
+	case ${#matches[@]} in
+		0) die "no package '${spec}' in ${preinstall_from}, pass name-version-revision or an archive" ;;
+		1) echo "${matches[0]}" ;;
+		*) die "several packages match '${spec}': ${matches[*]##*/}" ;;
+	esac
 }
 
 # The job phase runs on the cluster node, where the environment is ours to set.
@@ -420,6 +490,9 @@ if (( run_job )); then
 	else
 		echo "=== overlay:    no"
 	fi
+	for archive in ${preinstalls[@]+"${preinstalls[@]}"}; do
+		echo "=== preinstall: ${archive}"
+	done
 
 	export BEE_TMP_TMPDIR=${bee_tmpdir}
 	export BEE_TMP_BUILDROOT=${buildroot}
@@ -533,6 +606,21 @@ if (( run_job )); then
 
 	status=0
 	declare -a failed=()
+	for archive in ${preinstalls[@]+"${preinstalls[@]}"}; do
+		echo "=== [preinstall] ${archive##*/}: $(date '+%F %T') starting"
+		install_archive_into_overlay "${archive}"
+		rc=$?
+		echo "=== [preinstall] ${archive##*/}: $(date '+%F %T') install into the overlay exited with ${rc}"
+		if (( rc )); then
+			status=${rc}
+			failed+=("${archive##*/}")
+			# Every bee-file was meant to build against the pre-installed
+			# packages, so none is built without them, --keep-going or not.
+			echo "=== stopping, ${#beefiles[@]} bee-file(s) not built"
+			beefiles=()
+			break
+		fi
+	done
 	for (( i = 0; i < ${#beefiles[@]}; i++ )); do
 		beefile=${beefiles[i]}
 		echo "=== [$(( i + 1 ))/${#beefiles[@]}] ${beefile##*/}: $(date '+%F %T') starting"
@@ -576,6 +664,13 @@ if [[ ${stdout} == */* ]]; then
 fi
 [ ! -e "${stdout}" ] || echo "Note: overwriting the existing log file"
 
+# Resolve the packages to install up front, so that a typo fails now and not
+# after the job has waited in the queue.
+for (( i = 0; i < ${#preinstalls[@]}; i++ )); do
+	preinstalls[i]=$(resolve_preinstall "${preinstalls[i]}") || exit 1
+	echo "Pre-install: ${preinstalls[i]}" >&2
+done
+
 # Check the given working directory before staging, so that a typo does not
 # leave copies of the bee-files behind.
 if [ -n "${workdir}" ]; then
@@ -637,6 +732,9 @@ if (( overlay )); then
 		mxqsub+=(--overlay-dir="${dir}")
 	done
 	(( keep_overlay )) && mxqsub+=(--keep-overlay)
+	for archive in ${preinstalls[@]+"${preinstalls[@]}"}; do
+		mxqsub+=(--preinstall="${archive}")
+	done
 else
 	mxqsub+=(--no-overlay)
 fi