diff --git a/packages/metro/src/Server.js b/packages/metro/src/Server.js
index 4846da83e1..42e38011b2 100644
--- a/packages/metro/src/Server.js
+++ b/packages/metro/src/Server.js
@@ -1176,10 +1176,11 @@ export default class Server {
       };
     },
     finish({req, mres, serializerOptions, result, bundlePerfLogger}) {
+      const bundleByteLength = Buffer.byteLength(result.bundle);
       bundlePerfLogger.annotate({
         int: {
           bundle_length: result.bundle.length,
-          bundle_byte_length: Buffer.byteLength(result.bundle),
+          bundle_byte_length: bundleByteLength,
         },
       });
       mres.once('error', () => {
@@ -1219,10 +1220,7 @@ export default class Server {
         }
         mres.setHeader('Content-Type', 'application/javascript; charset=UTF-8');
         mres.setHeader('Last-Modified', result.lastModifiedDate.toUTCString());
-        mres.setHeader(
-          'Content-Length',
-          String(Buffer.byteLength(result.bundle)),
-        );
+        mres.setHeader('Content-Length', String(bundleByteLength));
         mres.end(result.bundle);
       }
     },