diff --git a/index.js b/index.js
index ca254d0c9761c8c02070eaf51675627a6d80ff46..efb522616b586f3c8692d5bafd4f2da7aa9b0e20 100644
--- a/index.js
+++ b/index.js
@@ -483,7 +483,7 @@ function fastifyOauth2 (fastify, options, next) {
 
     function onUserinfoResponse (res) {
       let rawData = ''
-      res.on('data', (chunk) => { rawData = chunk })
+      res.on('data', (chunk) => { rawData += chunk })
       res.on('end', () => {
         try {
           cb(null, JSON.parse(rawData)) // should always be JSON since we don't do jwt auth response