diff --git a/build-packages.sh b/build-packages.sh
index 846f0b6678e..95902dde90c 100755
--- a/build-packages.sh
+++ b/build-packages.sh
@@ -134,6 +134,43 @@ keep_apple_silicon_mkinitcpio_drop_ins() {
     fail "lost the limine-entry-tool.d cleanup in $pkgbuild"
 }
 
+# Upstream's omarchy-settings PKGBUILD installs its user units from an explicit
+# list rather than a glob, so a unit this fork adds under default/systemd/user/
+# ships under /usr/share/omarchy/default/ but never reaches
+# /usr/lib/systemd/user/, where first-run and the migration enable it. That is
+# what 4.0.2-2 did with the ambient keyboard backlight unit: every install got
+# a wants symlink to a unit systemd reports as not-found. Add an install line
+# for each fork unit right after upstream's own, and step aside for a unit
+# upstream has since adopted.
+readonly fork_user_units=(
+  omarchy-brightness-keyboard-auto.service
+)
+
+install_fork_user_units() {
+  local pkgbuild="$1" unit last line
+
+  for unit in "${fork_user_units[@]}"; do
+    [[ -f "$checkout/default/systemd/user/$unit" ]] ||
+      fail "default/systemd/user/$unit is listed in fork_user_units but missing from the checkout"
+    if grep -qF "default/systemd/user/$unit " "$pkgbuild"; then
+      continue
+    fi
+
+    # Fail loudly if upstream restructures this. Silently not matching would
+    # ship a package without the unit, which is the failure this exists to
+    # prevent and the one that only shows as a dangling symlink after install.
+    last=$(grep -nE '^[[:space:]]*install -Dm644 default/systemd/user/[^[:space:]]+\.service ' "$pkgbuild" |
+      tail -n 1 | cut -d: -f1)
+    [[ -n $last ]] ||
+      fail "omarchy-settings PKGBUILD no longer installs user units as expected; re-check it against $pkgbuild"
+
+    line="  install -Dm644 default/systemd/user/$unit \"\$pkgdir/usr/lib/systemd/user/$unit\""
+    awk -v n="$last" -v line="$line" '{ print } NR == n { print line }' "$pkgbuild" >"$pkgbuild.tmp" &&
+      mv "$pkgbuild.tmp" "$pkgbuild"
+    grep -qF "$line" "$pkgbuild" || fail "could not add $unit to $pkgbuild"
+  done
+}
+
 # makepkg runs with --nodeps because the runtime dependencies include packages
 # built here, so pacman cannot resolve them yet. That skips makedepends too,
 # leaving the build tools to be installed up front.
@@ -187,6 +224,7 @@ build_package() {
   fi
   if [[ $package == "omarchy-settings" ]]; then
     keep_apple_silicon_mkinitcpio_drop_ins "$build_dir/$package/PKGBUILD"
+    install_fork_user_units "$build_dir/$package/PKGBUILD"
   fi
   if [[ $package == "omarchy" || $package == "omarchy-settings" ]]; then
     set_pkgrel "$build_dir/$package/PKGBUILD"
diff --git a/test/shell.d/install-mac-test.sh b/test/shell.d/install-mac-test.sh
index 1067348521e..28b253a7dc0 100755
--- a/test/shell.d/install-mac-test.sh
+++ b/test/shell.d/install-mac-test.sh
@@ -64,6 +64,43 @@ if ! (
   fail "set_pkgrel no-ops without OMARCHY_PKGREL, writes a number, and rejects junk"
 fi
 rm -rf "$rel_dir"
+# Upstream's package() lists its user units one by one, so a unit only this
+# fork ships has to be added to that list or it never reaches
+# /usr/lib/systemd/user/ and the migration that enables it dangles.
+units_dir=$(mktemp -d)
+cat >"$units_dir/PKGBUILD" <<'PKG'
+package() {
+  install -Dm644 default/systemd/user/bt-agent.service "$pkgdir/usr/lib/systemd/user/bt-agent.service"
+  install -Dm644 default/systemd/user/omarchy-crash-watch.service "$pkgdir/usr/lib/systemd/user/omarchy-crash-watch.service"
+  install -d "$pkgdir/usr/share/omarchy/applications"
+}
+PKG
+if ! (
+  source "$build_script"
+  install_fork_user_units "$units_dir/PKGBUILD"
+  # A second pass, or upstream adopting the unit, must not add it twice.
+  install_fork_user_units "$units_dir/PKGBUILD"
+  added='install -Dm644 default/systemd/user/omarchy-brightness-keyboard-auto.service "$pkgdir/usr/lib/systemd/user/omarchy-brightness-keyboard-auto.service"'
+  [[ $(grep -cF "$added" "$units_dir/PKGBUILD") == 1 ]] || exit 1
+  # Directly after upstream's last unit, so it stays inside package().
+  grep -A1 -F 'omarchy-crash-watch.service' "$units_dir/PKGBUILD" | grep -qF "$added" || exit 1
+  printf 'package() {\n  install -d "$pkgdir/usr/share"\n}\n' >"$units_dir/PKGBUILD"
+  if ( install_fork_user_units "$units_dir/PKGBUILD" >/dev/null 2>&1 ); then
+    exit 1
+  fi
+); then
+  rm -rf "$units_dir"
+  fail "install_fork_user_units adds each fork unit once after upstream's units and refuses an unrecognised package()"
+fi
+rm -rf "$units_dir"
+pass "install_fork_user_units adds each fork unit once after upstream's units and refuses an unrecognised package()"
+
+grep -A3 'package == "omarchy-settings"' "$build_script" | grep -q install_fork_user_units ||
+  fail "the package build installs the fork's user units into omarchy-settings"
+grep -qF '  omarchy-brightness-keyboard-auto.service' "$build_script" ||
+  fail "the package build lists the ambient keyboard backlight unit as a fork unit"
+pass "the package build installs the fork's user units into omarchy-settings"
+
 grep -A2 'package == "omarchy-settings"' "$build_script" | grep -q set_pkgrel ||
   fail "the package build stamps pkgrel on omarchy and omarchy-settings"
 pass "the package build can stamp a Mac-only pkgrel on omarchy and omarchy-settings"