diff --git a/package.json b/package.json
index ed83e4d..be79f06 100644
--- a/package.json
+++ b/package.json
@@ -7,11 +7,12 @@
   "files": [
     ".idea/icon.svg",
     "README.md",
+    "scripts/postinstall.js",
     "src",
     "dist",
-    "*.js",
-    "*.d.ts",
-    "*.mjs",
+    "./*.js",
+    "./*.d.ts",
+    "./*.mjs",
     "!**/__utils__",
     "!**/__tests__",
     "!**/*.test.*"
@@ -60,6 +61,7 @@
   "scripts": {
     "prepare": "husky install || true",
     "prepack": "tsc",
+    "postinstall": "node scripts/postinstall.js",
     "build": "tsc",
     "build:e2e": "tsc && nyc instrument --in-place dist && npm pack && mv jest-metadata-*.tgz package.tar.gz",
     "docs": "typedoc",
diff --git a/scripts/postinstall.js b/scripts/postinstall.js
new file mode 100755
index 0000000..c855cda
--- /dev/null
+++ b/scripts/postinstall.js
@@ -0,0 +1,25 @@
+#!/usr/bin/env node
+
+const fs = require('node:fs');
+const path = require('node:path');
+const process = require('node:process');
+
+const instances = [];
+
+for (let cwd = process.cwd(); cwd !== path.dirname(cwd); cwd = path.dirname(cwd)) {
+  const anotherInstance = path.join(cwd, 'node_modules', 'jest-metadata');
+  if (fs.existsSync(anotherInstance)) {
+    instances.push(anotherInstance);
+  }
+}
+
+if (instances.length > 1) {
+  process.exitCode = 1;
+
+  console.error('\x1b[31m%s\x1b[0m', [
+    '[jest-metadata] postinstall script failed!',
+    'More than one instance of jest-metadata has been installed:',
+    ...instances.map((dir) => `- ${dir}`),
+    'Please flatten your package-lock.json or yarn.lock file to resolve this issue.',
+  ].join('\n'));
+}