diff --git a/packages/internal-helpers/package.json b/packages/internal-helpers/package.json
index 018b9d44cafc..feadc3dd8610 100644
--- a/packages/internal-helpers/package.json
+++ b/packages/internal-helpers/package.json
@@ -46,7 +46,8 @@
     "build": "astro-scripts build \"src/**/*.ts\" && tsc -p tsconfig.json",
     "build:ci": "astro-scripts build \"src/**/*.ts\"",
     "dev": "astro-scripts dev \"src/**/*.ts\"",
-    "test": "astro-scripts test \"test/**/*.test.js\""
+    "test": "astro-scripts test \"test/**/*.test.ts\"",
+    "typecheck:tests": "tsc -p tsconfig.test.json --noEmit"
   },
   "dependencies": {
     "picomatch": "^4.0.3"
diff --git a/packages/internal-helpers/test/create-filter.test.js b/packages/internal-helpers/test/create-filter.test.ts
similarity index 100%
rename from packages/internal-helpers/test/create-filter.test.js
rename to packages/internal-helpers/test/create-filter.test.ts
diff --git a/packages/internal-helpers/test/path.test.js b/packages/internal-helpers/test/path.test.ts
similarity index 99%
rename from packages/internal-helpers/test/path.test.js
rename to packages/internal-helpers/test/path.test.ts
index c4359f05a5fd..2981450c08b6 100644
--- a/packages/internal-helpers/test/path.test.js
+++ b/packages/internal-helpers/test/path.test.ts
@@ -652,7 +652,7 @@ describe('isParentDirectory', () => {
 	});
 
 	it('should correctly reject non-parent relationships', () => {
-		const invalidCases = [
+		const invalidCases: Array<[string, string]> = [
 			// Different directories
 			['/home', '/usr'],
 			['/home/user', '/home/otheruser'],
@@ -681,8 +681,11 @@ describe('isParentDirectory', () => {
 			['', '/home'],
 			['/home', ''],
 			['', ''],
+			// @ts-expect-error: expected to handle null/undefined gracefully
 			[null, '/home'],
+			// @ts-expect-error: expected to handle null/undefined gracefully
 			['/home', null],
+			// @ts-expect-error: expected to handle null/undefined gracefully
 			[undefined, '/home'],
 
 			// Same path (not parent-child)
diff --git a/packages/internal-helpers/test/request.test.js b/packages/internal-helpers/test/request.test.ts
similarity index 99%
rename from packages/internal-helpers/test/request.test.js
rename to packages/internal-helpers/test/request.test.ts
index 8741dbdddb62..2029367af9b9 100644
--- a/packages/internal-helpers/test/request.test.js
+++ b/packages/internal-helpers/test/request.test.ts
@@ -137,7 +137,7 @@ describe('getClientIpAddress', () => {
 	/**
 	 * Helper to create a minimal Request with given headers.
 	 */
-	function makeRequest(headers = {}) {
+	function makeRequest(headers: HeadersInit = {}) {
 		return new Request('https://example.com', { headers });
 	}
 
diff --git a/packages/internal-helpers/tsconfig.test.json b/packages/internal-helpers/tsconfig.test.json
new file mode 100644
index 000000000000..7d6bc4428b35
--- /dev/null
+++ b/packages/internal-helpers/tsconfig.test.json
@@ -0,0 +1,12 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "include": ["test/**/*.ts"],
+  "exclude": ["test/fixtures/**"],
+  "compilerOptions": {
+    "allowJs": true,
+    "noUnusedLocals": false,
+    "noUnusedParameters": false,
+    "rewriteRelativeImportExtensions": true
+  },
+  "references": [{ "path": "../astro/tsconfig.test.json" }]
+}