diff --git a/src/@types/module.d.ts b/src/@types/module.d.ts
index 496f156..e557f3e 100644
--- a/src/@types/module.d.ts
+++ b/src/@types/module.d.ts
@@ -12,7 +12,14 @@ declare module 'module' {
 	export const _extensions: NodeJS.RequireExtensions;
 	export function _resolveFilename(
 		request: string,
-		parent: any,
+		parent: {
+
+			/**
+			 * Can be null if the parent id is 'internal/preload' (e.g. via --require)
+			 * which doesn't have a file path.
+			 */
+			filename: string | null;
+		},
 		isMain: boolean,
 		options?: any,
 	): string;
diff --git a/src/index.ts b/src/index.ts
index 7f72ab4..5dcc41f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -136,7 +136,7 @@ Module._resolveFilename = function (request, parent, isMain, options) {
 		&& !isPathPattern.test(request)
 
 		// Dependency paths should not be resolved using tsconfig.json
-		&& !parent?.filename.includes(nodeModulesPath)
+		&& !parent?.filename?.includes(nodeModulesPath)
 	) {
 		const possiblePaths = tsconfigPathsMatcher(request);
 
diff --git a/tests/fixtures/tsconfig/src/resolve-target.ts b/tests/fixtures/tsconfig/src/resolve-target.ts
index 3e88556..421aa39 100644
--- a/tests/fixtures/tsconfig/src/resolve-target.ts
+++ b/tests/fixtures/tsconfig/src/resolve-target.ts
@@ -1 +1,2 @@
-export default 'resolve-target';
+console.log('resolve-target loaded');
+export default 'resolve-target value';
diff --git a/tests/specs/typescript/ts.ts b/tests/specs/typescript/ts.ts
index c7319c8..5093d50 100644
--- a/tests/specs/typescript/ts.ts
+++ b/tests/specs/typescript/ts.ts
@@ -54,6 +54,11 @@ export default testSuite(async ({ describe }, node: NodeApis) => {
 				assertResults(nodeProcess.stdout);
 				expect(nodeProcess.stdout).toMatch('{"default":1234}');
 			});
+
+			test('Require flag', async () => {
+				const nodeProcess = await node.requireFlag(importPath);
+				assertResults(nodeProcess.stdout);
+			});
 		});
 
 		describe('full path via .js', ({ test }) => {
diff --git a/tests/specs/typescript/tsconfig.ts b/tests/specs/typescript/tsconfig.ts
index 2b26611..47edd78 100644
--- a/tests/specs/typescript/tsconfig.ts
+++ b/tests/specs/typescript/tsconfig.ts
@@ -26,14 +26,21 @@ export default testSuite(async ({ describe }, node: NodeApis) => {
 				const nodeProcess = await node.load('./src/base-url.ts', {
 					cwd: './tsconfig',
 				});
-				expect(nodeProcess.stdout).toBe('resolve-target');
+				expect(nodeProcess.stdout).toBe('resolve-target loaded\nresolve-target value');
+			});
+
+			test('Require flag', async () => {
+				const nodeProcess = await node.requireFlag('resolve-target', {
+					cwd: './tsconfig',
+				});
+				expect(nodeProcess.stdout).toMatch('resolve-target loaded');
 			});
 
 			test('resolves paths exact match', async () => {
 				const nodeProcess = await node.load('./src/paths-exact-match.ts', {
 					cwd: './tsconfig',
 				});
-				expect(nodeProcess.stdout).toBe('resolve-target');
+				expect(nodeProcess.stdout).toBe('resolve-target loaded\nresolve-target value');
 			});
 
 			test('resolves paths prefix', async () => {
diff --git a/tests/utils/node-with-loader.ts b/tests/utils/node-with-loader.ts
index a1363be..f3dc496 100644
--- a/tests/utils/node-with-loader.ts
+++ b/tests/utils/node-with-loader.ts
@@ -1,6 +1,6 @@
 import fs from 'fs/promises';
 import path from 'path';
-import { execaNode } from 'execa';
+import { execaNode, execa } from 'execa';
 import getNode from 'get-node';
 
 type Options = {
@@ -11,6 +11,8 @@ type Options = {
 	nodeOptions?: string[];
 };
 
+const cjsLoaderPath = path.resolve(__dirname, '../..');
+
 export const nodeWithLoader = async (
 	options: Options,
 ) => await execaNode(
@@ -25,7 +27,7 @@ export const nodeWithLoader = async (
 			...(options.nodeOptions ?? []),
 
 			'--require',
-			path.resolve(__dirname, '../..'),
+			cjsLoaderPath,
 		],
 		nodePath: options.nodePath,
 		cwd: options.cwd,
@@ -129,6 +131,30 @@ export async function createNode(
 				cwd: fixturePath,
 			});
 		},
+		requireFlag(
+			filePath: string,
+			options?: {
+				cwd?: string;
+			},
+		) {
+			return execa(
+				node.path,
+				[
+					'--require',
+					cjsLoaderPath,
+					'--require',
+					filePath,
+					'--eval',
+					'null',
+				],
+				{
+					cwd: path.join(fixturePath, options?.cwd ?? ''),
+					env: {
+						ESBK_DISABLE_CACHE: '1',
+					},
+				},
+			);
+		},
 	};
 }