diff --git a/src/GuzzleHttp/Cache/DoctrineAdapter.php b/src/GuzzleHttp/Cache/DoctrineAdapter.php
index f3bcea93..baea4a24 100644
--- a/src/GuzzleHttp/Cache/DoctrineAdapter.php
+++ b/src/GuzzleHttp/Cache/DoctrineAdapter.php
@@ -46,7 +46,7 @@ private function getKey(RequestInterface $request)
             'method'  => $request->getMethod(),
             'uri'     => $request->getUrl(),
             'headers' => $request->getHeaders(),
-            'body'    => $request->getBody(),
+            'body'    => (string) $request->getBody(),
         ]));
     }
 }