diff --git a/scripts/inert-lo.sh b/scripts/inert-lo.sh
index 25f878c..08dd91d 100755
--- a/scripts/inert-lo.sh
+++ b/scripts/inert-lo.sh
@@ -3,7 +3,7 @@
 set -euo pipefail
 app=${1:?usage: scripts/inert-lo.sh path/to/LibreOffice.app}
 plist=$app/Contents/Info.plist
-[ -f "$plist" ] || { echo "inert-lo.sh: no $plist" >&2; exit 1; }
+plutil -lint -s "$plist" || { echo "inert-lo.sh: $plist is missing or unreadable" >&2; exit 1; }
 lsregister=/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister
 for key in CFBundleDocumentTypes CFBundleURLTypes UTExportedTypeDeclarations UTImportedTypeDeclarations; do
   if /usr/libexec/PlistBuddy -c "Print :$key" "$plist" >/dev/null 2>&1; then
diff --git a/tests/scripts/lo-unregistered.sh b/tests/scripts/lo-unregistered.sh
index eb25183..bda096f 100755
--- a/tests/scripts/lo-unregistered.sh
+++ b/tests/scripts/lo-unregistered.sh
@@ -14,6 +14,15 @@ if [ -d "$app" ]; then
 fi
 work=$(mktemp -d)
 trap 'rm -rf "$work"' EXIT
+fake=$work/a/b/Fake.app
+mkdir -p "$fake/Contents/PlugIns"
+echo "not a plist" >"$fake/Contents/Info.plist"
+! "$root/scripts/inert-lo.sh" "$fake" 2>/dev/null || fail "inert-lo.sh accepts an unreadable Info.plist"
+plutil -create xml1 "$fake/Contents/Info.plist"
+plutil -insert CFBundleDocumentTypes -array "$fake/Contents/Info.plist"
+"$root/scripts/inert-lo.sh" "$fake" >/dev/null
+! /usr/libexec/PlistBuddy -c "Print :CFBundleDocumentTypes" "$fake/Contents/Info.plist" >/dev/null 2>&1 || fail "inert-lo.sh left a claim"
+[ ! -e "$fake/Contents/PlugIns" ] || fail "inert-lo.sh left the plug-ins"
 for ext in docx xlsx pptx odt csv; do : >"$work/sample.$ext"; done
 cat >"$work/open.swift" <<'SWIFT'
 import AppKit