diff --git a/CHANGELOG.md b/CHANGELOG.md
index d3e823b..1482e2e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -56,6 +56,12 @@ All notable changes to this project will be documented in this file, in reverse
 
 ### Changed
 
+- [#41](https://github.com/zendframework/ZendService_Twitter/pull/41) modifies
+  how the `Twitter` class sends `POST` requests to send JSON payloads instead of
+  `application/x-www-form-urlencoded`. All payloads except those for media
+  uploads support this, and several newer endpoints (such as methods for
+  allowing direct message media attachments) now require them.
+
 - [#40](https://github.com/zendframework/ZendService_Twitter/pull/40) updates
   direct message support to set the character limit to 10k, as documented
   currently for the Twitter API.
diff --git a/library/ZendService/Twitter/Twitter.php b/library/ZendService/Twitter/Twitter.php
index f0d73ec..052885f 100644
--- a/library/ZendService/Twitter/Twitter.php
+++ b/library/ZendService/Twitter/Twitter.php
@@ -106,6 +106,13 @@ class Twitter
      */
     protected $username;
 
+    /**
+     * Flags to use with json_encode for POST requests
+     *
+     * @var int
+     */
+    private $jsonFlags = JSON_PRESERVE_ZERO_FRACTION | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE;
+
     /**
      * @param  null|array|Traversable $options
      * @param  null|OAuth\Consumer $consumer
@@ -1233,7 +1240,7 @@ protected function post($path, $data = null)
      *
      * Performs a POST or PUT request. Any data provided is set in the HTTP
      * client. String data is pushed in as raw POST data; array or object data
-     * is pushed in as POST parameters.
+     * is JSON-encoded before being passed to the request body.
      *
      * @param mixed $method
      * @param mixed $data
@@ -1241,11 +1248,17 @@ protected function post($path, $data = null)
      */
     protected function performPost($method, $data, Http\Client $client)
     {
-        if (is_string($data)) {
-            $client->setRawData($data);
-        } elseif (is_array($data) || is_object($data)) {
-            $client->setParameterPost((array) $data);
+        if (is_array($data) || is_object($data)) {
+            $data = json_encode($data, $this->jsonFlags);
         }
+
+        if (! empty($data)) {
+            $client->setRawBody($data);
+            $client->getRequest()
+                ->getHeaders()
+                ->addHeaderLine('Content-Type', 'application/json');
+        }
+
         $client->setMethod($method);
         return $client->send();
     }
diff --git a/tests/ZendService/Twitter/TwitterTest.php b/tests/ZendService/Twitter/TwitterTest.php
index 5e69508..c663eaf 100644
--- a/tests/ZendService/Twitter/TwitterTest.php
+++ b/tests/ZendService/Twitter/TwitterTest.php
@@ -12,6 +12,7 @@
 
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use ReflectionProperty;
 use Zend\Http;
 use ZendOAuth\Client as OAuthClient;
 use ZendOAuth\Consumer as OAuthConsumer;
@@ -25,6 +26,14 @@
 
 class TwitterTest extends TestCase
 {
+    public function setUp()
+    {
+        $twitter = new Twitter\Twitter();
+        $r = new ReflectionProperty($twitter, 'jsonFlags');
+        $r->setAccessible(true);
+        $this->jsonFlags = $r->getValue($twitter);
+    }
+
     /**
      * Quick reusable OAuth client stub setup. Its purpose is to fake
      * HTTP interactions with Twitter so the component can focus on what matters:
@@ -58,9 +67,18 @@ protected function stubOAuthClient(
         $client->setHeaders(['Accept-Charset' => 'ISO-8859-1,utf-8'])->will([$client, 'reveal']);
         $client->clearCookies()->will([$client, 'reveal']);
         $client->getCookies()->willReturn([]);
-        if (null !== $params) {
-            $setter = 'setParameter' . ucfirst(strtolower($method));
-            $client->$setter($params)->shouldBeCalled();
+        if (null !== $params && $method === 'GET') {
+            $client->setParameterGet($params)->shouldBeCalled();
+        }
+        if (null !== $params && $method === 'POST') {
+            $requestBody = json_encode($params, $this->jsonFlags);
+            $client->setRawBody($requestBody)->shouldBeCalled();
+
+            $headers = $this->prophesize(Http\Headers::class);
+            $headers->addHeaderLine('Content-Type', 'application/json')->shouldBeCalled();
+            $request = $this->prophesize(Http\Request::class);
+            $request->getHeaders()->will([$headers, 'reveal']);
+            $client->getRequest()->will([$request, 'reveal']);
         }
 
         $response = $this->prophesize(Http\Response::class);