diff --git a/appengine/flexible/mailjet/composer.json b/appengine/flexible/mailjet/composer.json
index f53d7ac15c..e447fed11c 100644
--- a/appengine/flexible/mailjet/composer.json
+++ b/appengine/flexible/mailjet/composer.json
@@ -2,7 +2,7 @@
     "require": {
         "silex/silex": "^1.3",
         "mailjet/mailjet-apiv3-php": "^1.1",
-        "guzzlehttp/guzzle": "~6.1.0"
+        "guzzlehttp/guzzle": "~6.5.8"
     },
     "require-dev": {
         "symfony/browser-kit": "^3.0",