diff --git a/fixtures/flight-esm/server/region.js b/fixtures/flight-esm/server/region.js
index fe992b6daf538..707e5195681ea 100644
--- a/fixtures/flight-esm/server/region.js
+++ b/fixtures/flight-esm/server/region.js
@@ -125,6 +125,10 @@ if (process.env.NODE_ENV === 'development') {
     try {
       res.set('Content-type', 'application/json');
       let requestedFilePath = req.query.name;
+      if (typeof requestedFilePath !== 'string') {
+        res.status(400).send("Bad request");
+        return;
+      }
 
       let isCompiledOutput = false;
       if (requestedFilePath.startsWith('file://')) {