diff --git a/composer.json b/composer.json
index 61bc460..d0d55fc 100644
--- a/composer.json
+++ b/composer.json
@@ -2,7 +2,7 @@
     "name": "mailgun/mailgun-php",
     "description": "The Mailgun SDK provides methods for all API functions.",
     "require": {
-        "guzzlehttp/guzzle": "~5.0"
+        "guzzlehttp/guzzle": "~6.0"
     },
     "require-dev": {
         "php": ">=5.4.0",