diff --git a/composer.json b/composer.json
index b07899b0..8852f6fa 100644
--- a/composer.json
+++ b/composer.json
@@ -46,7 +46,7 @@
         "psr/http-factory": "^1",
         "psr/http-factory-implementation": "^1",
         "symfony/http-foundation": "^2.1||^3||^4",
-        "zendframework/zend-diactoros": "^2.1"
+        "nyholm/psr7": "^1"
     },
     "require-dev": {
         "omnipay/tests": "^3",
diff --git a/tests/Omnipay/Common/Http/ClientTest.php b/tests/Omnipay/Common/Http/ClientTest.php
index bb14adad..c17a9cfc 100644
--- a/tests/Omnipay/Common/Http/ClientTest.php
+++ b/tests/Omnipay/Common/Http/ClientTest.php
@@ -61,7 +61,7 @@ public function testSendPostJson()
                     return false;
                 }
 
-                if ($request->getBody()->getContents() !== '{foo:bar}') {
+                if ((string) $request->getBody() !== '{foo:bar}') {
                     return false;
                 }