diff --git a/composer.json b/composer.json
index 69e08ec..26bac8b 100644
--- a/composer.json
+++ b/composer.json
@@ -14,7 +14,8 @@
   ],
   "require": {
     "php": ">=5.5.0",
-    "guzzlehttp/guzzle": "^6.0 || ^7.0"
+    "guzzlehttp/guzzle": "^6.0 || ^7.0",
+    "guzzlehttp/psr7": "^1.7.0"
   },
   "require-dev": {
     "phpunit/phpunit": "^4.8.36 || ^5.0",