diff --git a/install.ps1 b/install.ps1
index 22a70e0cc..f03e398f7 100644
--- a/install.ps1
+++ b/install.ps1
@@ -123,7 +123,14 @@
           # still open when it was pruned) is the usual cause.
           if (Test-Path -LiteralPath $dest) { throw "$dest is in the way; remove it and run this again" }
           Step "Installing Agent Office $tag"
-          # Exactly the dependency versions the release was tested with (its npm-shrinkwrap.json).
+          # Exactly the dependency versions the release was tested with (its npm-shrinkwrap.json). npm
+          # 12's `npm ci` reads only package-lock.json and refuses a package with just a shrinkwrap
+          # (#278), so give it the same file under that name too; older npm read the shrinkwrap first.
+          $shrinkwrap = Join-Path $pkg 'npm-shrinkwrap.json'
+          $lockfile = Join-Path $pkg 'package-lock.json'
+          if ((Test-Path -LiteralPath $shrinkwrap) -and -not (Test-Path -LiteralPath $lockfile)) {
+            Copy-Item -LiteralPath $shrinkwrap -Destination $lockfile
+          }
           Push-Location -LiteralPath $pkg
           # Out-Host, or npm's output would become part of this function's return value.
           try { & $npm ci --omit=dev --no-audit --no-fund --loglevel=error | Out-Host } finally { Pop-Location }
diff --git a/install.sh b/install.sh
index acf860d79..cbdf6c7f9 100755
--- a/install.sh
+++ b/install.sh
@@ -96,7 +96,12 @@ install_release() {
   dest="$VERSIONS/$tag"
   if [ ! -f "$dest/.installed" ]; then
     step "Installing Agent Office $tag"
-    # Exactly the dependency versions the release was tested with (its npm-shrinkwrap.json).
+    # Exactly the dependency versions the release was tested with (its npm-shrinkwrap.json). npm 12's
+    # `npm ci` reads only package-lock.json and refuses a package with just a shrinkwrap (#278), so
+    # give it the same file under that name too; older npm read the shrinkwrap first either way.
+    if [ -f "$STAGE/package/npm-shrinkwrap.json" ] && [ ! -e "$STAGE/package/package-lock.json" ]; then
+      cp "$STAGE/package/npm-shrinkwrap.json" "$STAGE/package/package-lock.json"
+    fi
     (cd "$STAGE/package" && npm ci --omit=dev --no-audit --no-fund --loglevel=error >&2) ||
       die "npm couldn't install Agent Office's dependencies (see above)"
     touch "$STAGE/package/.installed"
diff --git a/tests/install.test.ts b/tests/install.test.ts
new file mode 100644
index 000000000..516232a77
--- /dev/null
+++ b/tests/install.test.ts
@@ -0,0 +1,63 @@
+// install.sh against a local release tarball (AGENT_OFFICE_TARBALL), with a stand-in npm so nothing
+// is downloaded. Releases ship their dependency versions as npm-shrinkwrap.json (release.yml).
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { execFileSync } from 'node:child_process';
+import { chmodSync, existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+
+const script = path.join(import.meta.dirname, '..', 'install.sh');
+
+// A stand-in for npm 12, whose `npm ci` reads only package-lock.json: a package with just an
+// npm-shrinkwrap.json fails with the error from #278. It notes which lockfiles each `ci` saw.
+const FAKE_NPM = `#!/bin/sh
+[ "$1" = ci ] || exit 0
+echo "ci shrinkwrap=$([ -f npm-shrinkwrap.json ] && echo yes || echo no) lock=$([ -f package-lock.json ] && echo yes || echo no)" >>"$FAKE_NPM_LOG"
+if [ ! -f package-lock.json ]; then
+  echo "npm error code EUSAGE" >&2
+  echo "npm error The \\\`npm ci\\\` command can only install with an existing package-lock.json" >&2
+  exit 1
+fi
+`;
+
+test('install.sh installs a release whose lockfile is npm-shrinkwrap.json with an npm that reads only package-lock.json (#278)', (t) => {
+  const root = mkdtempSync(path.join(tmpdir(), 'agent-office-install-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+
+  const pkg = path.join(root, 'release', 'package');
+  mkdirSync(path.join(pkg, 'bin'), { recursive: true });
+  writeFileSync(path.join(pkg, 'package.json'), JSON.stringify({ name: 'agent-office', version: '0.1.999' }));
+  const shrinkwrap = JSON.stringify({ name: 'agent-office', version: '0.1.999', lockfileVersion: 3, packages: {} });
+  writeFileSync(path.join(pkg, 'npm-shrinkwrap.json'), shrinkwrap);
+  writeFileSync(path.join(pkg, 'bin', 'agent-office.js'), '');
+  const tarball = path.join(root, 'agent-office.tgz');
+  execFileSync('tar', ['-czf', tarball, '-C', path.join(root, 'release'), 'package']);
+
+  const bin = path.join(root, 'bin');
+  mkdirSync(bin);
+  writeFileSync(path.join(bin, 'npm'), FAKE_NPM);
+  chmodSync(path.join(bin, 'npm'), 0o755);
+  const log = path.join(root, 'npm.log');
+  const installDir = path.join(root, 'office');
+
+  execFileSync('bash', [script], {
+    env: {
+      ...process.env,
+      PATH: `${bin}${path.delimiter}${process.env.PATH}`,
+      HOME: root,
+      AGENT_OFFICE_TARBALL: tarball,
+      AGENT_OFFICE_INSTALL_DIR: installDir,
+      AGENT_OFFICE_BIN_DIR: '',
+      AGENT_OFFICE_INSTALL_ONLY: '1',
+      FAKE_NPM_LOG: log,
+    },
+    stdio: ['ignore', 'pipe', 'pipe'],
+  });
+
+  assert.equal(readFileSync(log, 'utf8'), 'ci shrinkwrap=yes lock=yes\n', 'npm ci sees the release lockfile under both names');
+  const installed = path.join(installDir, 'versions', 'v0.1.999');
+  assert.ok(existsSync(path.join(installed, '.installed')), 'the release is installed');
+  assert.equal(readFileSync(path.join(installed, 'package-lock.json'), 'utf8'), shrinkwrap, 'package-lock.json is the shrinkwrap');
+  assert.equal(readFileSync(path.join(installDir, 'current'), 'utf8'), 'v0.1.999\n');
+});