diff --git a/Makefile.am b/Makefile.am
index 5ba0dab2..43c9a336 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -53,6 +53,7 @@ EXTRA_DIST = \
 	PACKAGERS \
 	TODO \
 	autogen.sh \
+	build-aux/license-check.sh \
 	build-aux/manconv.sh \
 	build-aux/version.sh \
 	po/xz.pot-header
diff --git a/build-aux/license-check.sh b/build-aux/license-check.sh
new file mode 100644
index 00000000..f352e1c8
--- /dev/null
+++ b/build-aux/license-check.sh
@@ -0,0 +1,174 @@
+#!/bin/sh
+# SPDX-License-Identifier: 0BSD
+
+###############################################################################
+#
+# Look for missing license info in xz.git
+#
+# The project doesn't conform to the FSFE REUSE specification for now.
+# Instead, this script helps in finding files that lack license info.
+# Pass -v as an argument to get license info from all files in xz.git or,
+# when .git isn't available, from files extracted from a release tarball
+# (in case of a release tarball, the tree must be clean of any extra files).
+#
+# NOTE: This uses grep and xargs with options that aren't in POSIX.
+#
+###############################################################################
+#
+# Author: Lasse Collin
+#
+###############################################################################
+
+# Print good files too if -v is passed as an argument.
+VERBOSE=false
+case $1 in
+	'')
+		;;
+	-v)
+		VERBOSE=true
+		;;
+	*)
+		echo "Usage: $0 [-v]"
+		exit 1
+		;;
+esac
+
+
+# Use the C locale so that sorting is always the same.
+LC_ALL=C
+export LC_ALL
+
+
+# String to match the SPDX license identifier tag.
+# Spell it here in a way that doesn't match regular grep patterns.
+SPDX_LI='SPDX''-License-''Identifier'':'
+
+# Pattern for files that don't contain SPDX tags but they are under
+# a free license that isn't 0BSD.
+PAT_UNTAGGED_MISC='^COPYING\.
+^INSTALL\.generic$'
+
+# Pattern for files that are 0BSD but don't contain SPDX tags.
+# (The two file format specification files are public domain but
+# they can be treated as 0BSD too.)
+PAT_UNTAGGED_0BSD='^(.*/)?\.gitattributes$
+^(.*/)?\.gitignore$
+^\.github/SECURITY\.md$
+^AUTHORS$
+^COPYING$
+^ChangeLog$
+^INSTALL$
+^NEWS$
+^PACKAGERS$
+^(.*/)?README$
+^THANKS$
+^TODO$
+^(.*/)?[^/]+\.txt$
+^po/LINGUAS$
+^tests/xzgrep_expected_output$
+^tests/files/[^/]+\.(lz|lzma|xz)$'
+
+# Pattern for files that must be ignored when Git isn't available. This is
+# useful when this script is run right after extracting a release tarball.
+PAT_TARBALL_IGNORE='^(m4/)?[^/]*\.m4$
+^(.*/)?Makefile\.in(\.in)?$
+^(po|po4a)/.*[^.]..$
+^ABOUT-NLS$
+^build-aux/(config\..*|ltmain\.sh|[^.]*)$
+^config\.h\.in$
+^configure$'
+
+
+# Go to the top source dir.
+cd "$(dirname "$0")/.." || exit 1
+
+# Get the list of files to check from git if possible.
+# Otherwise list the whole source tree. This script should pass
+# if it is run right after extracting a release tarball.
+if test -d .git && type git > /dev/null 2>&1; then
+	FILES=$(git ls-files) || exit 1
+	IS_TARBALL=false
+else
+	FILES=$(find . -type f) || exit 1
+	FILES=$(printf '%s\n' "$FILES" | sed 's,^\./,,')
+	IS_TARBALL=true
+fi
+
+# Sort to keep the order consistent.
+FILES=$(printf '%s\n' "$FILES" | sort)
+
+
+# Find the tagged files.
+TAGGED=$(printf '%s\n' "$FILES" | xargs -r -d '\n' grep -l "$SPDX_LI")
+
+# Find the tagged 0BSD files.
+TAGGED_0BSD=$(printf '%s\n' "$TAGGED" \
+	| xargs -r -d '\n' grep -l "$SPDX_LI 0BSD")
+
+# Find the tagged non-0BSD files, that is, remove the 0BSD-tagged files
+# from the list of tagged files.
+TAGGED_MISC=$(printf '%s\n%s\n' "$TAGGED" "$TAGGED_0BSD" | sort | uniq -u)
+
+
+# Remove the tagged files from the list.
+FILES=$(printf '%s\n%s\n' "$FILES" "$TAGGED" | sort | uniq -u)
+
+# Find the intentionally-untagged files.
+UNTAGGED_0BSD=$(printf '%s\n' "$FILES" | grep -E "$PAT_UNTAGGED_0BSD")
+UNTAGGED_MISC=$(printf '%s\n' "$FILES" | grep -E "$PAT_UNTAGGED_MISC")
+
+# Remove the intentionally-untagged files from the list.
+FILES=$(printf '%s\n' "$FILES" | grep -Ev \
+	-e "$PAT_UNTAGGED_0BSD" -e "$PAT_UNTAGGED_MISC")
+
+
+# FIXME: Allow untagged translations if they have a public domain notice.
+# These are old translations that haven't been updated after 2024-02-14.
+# Eventually these should go away.
+PD_PO=$(printf '%s\n' "$FILES" | grep '\.po$' | \
+	xargs -r -d '\n' grep -Fl '# This file is put in the public domain.')
+
+if test -n "$PD_PO"; then
+	# Remove the public domain .po files from the list.
+	FILES=$(printf '%s\n%s\n' "$FILES" "$PD_PO" | sort | uniq -u)
+fi
+
+
+# Remove generated files from the list which don't have SPDX tags but which
+# can be present in release tarballs. This step is skipped when the file list
+# is from "git ls-files".
+GENERATED=
+if $IS_TARBALL; then
+	GENERATED=$(printf '%s\n' "$FILES" | grep -E "$PAT_TARBALL_IGNORE")
+	FILES=$(printf '%s\n' "$FILES" | grep -Ev "$PAT_TARBALL_IGNORE")
+fi
+
+
+if $VERBOSE; then
+	printf '# Tagged 0BSD files:\n%s\n\n' "$TAGGED_0BSD"
+	printf '# Intentionally untagged 0BSD:\n%s\n\n' "$UNTAGGED_0BSD"
+
+	# FIXME: Remove when no longer needed.
+	if test -n "$PD_PO"; then
+		printf '# Old public domain translations:\n%s\n\n' "$PD_PO"
+	fi
+
+	printf '# Tagged non-0BSD files:\n%s\n\n' "$TAGGED_MISC"
+	printf '# Intentionally untagged miscellaneous: \n%s\n\n' \
+		"$UNTAGGED_MISC"
+
+	if test -n "$GENERATED"; then
+		printf '# Generated files whose license was NOT checked:\n%s\n\n' \
+			"$GENERATED"
+	fi
+fi
+
+
+# Look for files with an unknown license and set the exit status accordingly.
+STATUS=0
+if test -n "$UNTAGGED"; then
+	printf '# ERROR: Licensing is unclear:\n%s\n' "$UNTAGGED"
+	STATUS=1
+fi
+
+exit "$STATUS"