diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d00a208..008b779 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -86,6 +86,9 @@ jobs:
       - name: Ultracite check
         working-directory: npm
         run: npm run check
+      - name: Installer tests
+        working-directory: npm
+        run: npm test
   npm-package-smoke:
     runs-on: ubuntu-latest
     steps:
diff --git a/npm/package.json b/npm/package.json
index 4127f97..04de263 100644
--- a/npm/package.json
+++ b/npm/package.json
@@ -30,7 +30,8 @@
   "scripts": {
     "check": "ultracite check",
     "fix": "ultracite fix",
-    "postinstall": "node scripts/install.js"
+    "postinstall": "node scripts/install.js",
+    "test": "node scripts/install.test.js"
   },
   "devDependencies": {
     "@biomejs/biome": "2.5.6",
diff --git a/npm/scripts/install.js b/npm/scripts/install.js
index 7875c5c..c46c672 100644
--- a/npm/scripts/install.js
+++ b/npm/scripts/install.js
@@ -1,6 +1,6 @@
 #!/usr/bin/env node
 
-const { execSync } = require("node:child_process");
+const { execFileSync } = require("node:child_process");
 const fs = require("node:fs");
 const http = require("node:http");
 const https = require("node:https");
@@ -79,7 +79,7 @@ function extractTarGz(buffer, destDir) {
   fs.writeFileSync(tmpFile, buffer);
 
   try {
-    execSync(`tar xzf "${tmpFile}" -C "${destDir}"`, { stdio: "pipe" });
+    execFileSync("tar", ["xzf", tmpFile, "-C", destDir], { stdio: "pipe" });
   } finally {
     try {
       fs.unlinkSync(tmpFile);
@@ -94,7 +94,7 @@ function extractZip(buffer, destDir) {
   fs.writeFileSync(tmpFile, buffer);
 
   try {
-    execSync(`unzip -o "${tmpFile}" -d "${destDir}"`, { stdio: "pipe" });
+    execFileSync("unzip", ["-o", tmpFile, "-d", destDir], { stdio: "pipe" });
   } finally {
     try {
       fs.unlinkSync(tmpFile);
@@ -166,7 +166,11 @@ async function install() {
   }
 }
 
-install().catch((error) => {
-  console.error("Installation failed:", error.message);
-  process.exit(1);
-});
+if (require.main === module) {
+  install().catch((error) => {
+    console.error("Installation failed:", error.message);
+    process.exit(1);
+  });
+}
+
+module.exports = { extractTarGz, extractZip };
diff --git a/npm/scripts/install.test.js b/npm/scripts/install.test.js
new file mode 100644
index 0000000..dc6d401
--- /dev/null
+++ b/npm/scripts/install.test.js
@@ -0,0 +1,35 @@
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+const test = require("node:test");
+const { execFileSync } = require("node:child_process");
+
+const { extractTarGz } = require("./install");
+
+test("extractTarGz treats destination paths as literal arguments", (t) => {
+  const root = fs.mkdtempSync(
+    path.join(os.tmpdir(), "code-memory-install-test-")
+  );
+  t.after(() => fs.rmSync(root, { force: true, recursive: true }));
+
+  const source = path.join(root, "source");
+  const destination = path.join(root, "$(touch injected)");
+  const archive = path.join(root, "fixture.tar.gz");
+  fs.mkdirSync(source);
+  fs.mkdirSync(destination);
+  fs.writeFileSync(path.join(source, "code-memory"), "fixture");
+  execFileSync("tar", ["czf", archive, "-C", source, "code-memory"]);
+
+  extractTarGz(fs.readFileSync(archive), destination);
+
+  assert.equal(
+    fs.readFileSync(path.join(destination, "code-memory"), "utf8"),
+    "fixture"
+  );
+  assert.equal(
+    fs.existsSync(path.join(process.cwd(), "injected")),
+    false,
+    "archive extraction must not execute shell syntax from paths"
+  );
+});