diff --git a/composer.json b/composer.json
index 0d1fe6db..c1f5e38e 100644
--- a/composer.json
+++ b/composer.json
@@ -19,6 +19,7 @@
         "composer/package-versions-deprecated": "1.11.99.2",
         "elife/api-client": "^1.0",
         "guzzlehttp/promises": "^1.0",
+        "guzzlehttp/psr7": "^1.0",
         "symfony/serializer": "^2.8.2 || ^3.0.2"
     },
     "require-dev": {