diff --git a/client/src/Plugin/QueueWorker/CollectClientQueueWorker.php b/client/src/Plugin/QueueWorker/CollectClientQueueWorker.php
index d1a35d8..d62c4b3 100644
--- a/client/src/Plugin/QueueWorker/CollectClientQueueWorker.php
+++ b/client/src/Plugin/QueueWorker/CollectClientQueueWorker.php
@@ -16,10 +16,9 @@ use Drupal\Core\Queue\QueueWorkerBase;
 use Drupal\Core\Queue\SuspendQueueException;
 use GuzzleHttp\ClientInterface;
 use GuzzleHttp\Exception\RequestException;
-use GuzzleHttp\Message\ResponseInterface;
+use Psr\Http\Message\ResponseInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
-use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Serializer\SerializerInterface;
 
 /**
@@ -231,7 +230,7 @@ class CollectClientQueueWorker extends QueueWorkerBase implements ContainerFacto
     // Special support for CollectJSON field definition.
     try {
       foreach ($this->getTransferObjects($item) as $item_values) {
-        $response = $this->httpClient->post($url, array_merge($item_values, $options));
+        $response = $this->httpClient->request('POST', $url, array_merge($item_values, $options));
         if ($response->getStatusCode() != 201) {
           throw new \Exception('Expected status code 201 Created, got ' . $response->getStatusCode() . ' ' . $response->getReasonPhrase() . ' when submitting item to ' . $url . '.', 0);
         }
@@ -263,7 +262,7 @@ class CollectClientQueueWorker extends QueueWorkerBase implements ContainerFacto
    *
    * @param string $cache_key
    *   The entity cache key.
-   * @param \GuzzleHttp\Message\ResponseInterface $response
+   * @param \Psr\Http\Message\ResponseInterface $response
    *   The response.
    */
   protected function cacheUuid($cache_key, ResponseInterface $response) {
@@ -282,8 +281,12 @@ class CollectClientQueueWorker extends QueueWorkerBase implements ContainerFacto
    */
   protected function parseResponse(ResponseInterface $response, $property) {
     try {
+      if (!$response->getBody()) {
+        return FALSE;
+      }
+
       // Decode received data.
-      $json = $response->json();
+      $json = json_decode($response->getBody()->getContents(), TRUE);
 
       if ($property == 'uuid') {
         return isset($json['data'][$property]) ? $json['data'][$property] : FALSE;
diff --git a/client/tests/src/Unit/Plugin/QueueWorker/QueueWorkerTest.php b/client/tests/src/Unit/Plugin/QueueWorker/QueueWorkerTest.php
index 6dca1e9..777b591 100644
--- a/client/tests/src/Unit/Plugin/QueueWorker/QueueWorkerTest.php
+++ b/client/tests/src/Unit/Plugin/QueueWorker/QueueWorkerTest.php
@@ -215,10 +215,10 @@ EOF;
     );
     $url = 'http://example.com/collect/api/v1/submissions';
     $location = 'http://server.collect.dev/collect/api/v1/submissions/f67c88c9-1608-4f47-8291-4e35411af61f';
-    $response = $this->getMock('GuzzleHttp\Message\ResponseInterface');
+    $response = $this->getMock('Psr\Http\Message\ResponseInterface');
     $this->httpClient->expects($this->once())
-      ->method('post')
-      ->with($url, $options)
+      ->method('request')
+      ->with('POST', $url, $options)
       ->will($this->returnValue($response));
 
     $response->expects($this->once())