diff --git a/composer.json b/composer.json
index bd5f3db..fdb3a60 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,8 @@
     },
     "require-dev": {
         "phpunit/phpunit": "~4.8",
-        "php-http/guzzle6-adapter": "^1.0"
+        "php-http/guzzle6-adapter": "^1.0",
+        "guzzlehttp/psr7": "^1.4"
     },
     "autoload": {
         "psr-0": {