diff --git a/lib/server-request.js b/lib/server-request.js
index 7b67012..70ff9e6 100644
--- a/lib/server-request.js
+++ b/lib/server-request.js
@@ -23,7 +23,7 @@ class ServerRequest {
   send(options) {
     return new Promise((resolve, reject) => {
       if (options.method === 'POST' || options.method === 'PUT') {
-        options.headers['content-length'] = options.body.length;
+        options.headers['content-length'] = Buffer.byteLength(options.body, 'utf8');
       } else {
         delete options.body;
       }