diff --git a/lib/platform-shims/esm.mjs b/lib/platform-shims/esm.mjs
index 92f2f0993..c25baa5a3 100644
--- a/lib/platform-shims/esm.mjs
+++ b/lib/platform-shims/esm.mjs
@@ -21,7 +21,7 @@ try {
 } catch (e) {
   __dirname = process.cwd();
 }
-const mainFilename = __dirname.split('node_modules')[0]
+const mainFilename = __dirname.substring(0, __dirname.lastIndexOf('node_modules'));
 
 export default {
   assert: {