diff --git a/src/Mailgun/Assert.php b/src/Mailgun/Assert.php
index 68afc50..e5cbf6d 100644
--- a/src/Mailgun/Assert.php
+++ b/src/Mailgun/Assert.php
@@ -16,7 +16,7 @@ use Mailgun\Exception\InvalidArgumentException;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-class Assert extends \Webmozart\Assert\Assert
+final class Assert extends \Webmozart\Assert\Assert
 {
     protected static function reportInvalidArgument($message)
     {
diff --git a/src/Mailgun/HttpClient/Plugin/History.php b/src/Mailgun/HttpClient/Plugin/History.php
index ff2de8f..53105b8 100644
--- a/src/Mailgun/HttpClient/Plugin/History.php
+++ b/src/Mailgun/HttpClient/Plugin/History.php
@@ -19,7 +19,7 @@ use Psr\Http\Message\ResponseInterface;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-class History implements Journal
+final class History implements Journal
 {
     /**
      * @var ResponseInterface
diff --git a/src/Mailgun/HttpClientConfigurator.php b/src/Mailgun/HttpClientConfigurator.php
index e1a7524..7438c0e 100644
--- a/src/Mailgun/HttpClientConfigurator.php
+++ b/src/Mailgun/HttpClientConfigurator.php
@@ -22,7 +22,7 @@ use Mailgun\HttpClient\Plugin\History;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-class HttpClientConfigurator
+final class HttpClientConfigurator
 {
     /**
      * @var string
diff --git a/src/Mailgun/Hydrator/ArrayHydrator.php b/src/Mailgun/Hydrator/ArrayHydrator.php
index 98be108..700be80 100644
--- a/src/Mailgun/Hydrator/ArrayHydrator.php
+++ b/src/Mailgun/Hydrator/ArrayHydrator.php
@@ -17,7 +17,7 @@ use Psr\Http\Message\ResponseInterface;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-class ArrayHydrator implements Hydrator
+final class ArrayHydrator implements Hydrator
 {
     /**
      * @param ResponseInterface $response
diff --git a/src/Mailgun/Hydrator/ModelHydrator.php b/src/Mailgun/Hydrator/ModelHydrator.php
index 580b190..595518a 100644
--- a/src/Mailgun/Hydrator/ModelHydrator.php
+++ b/src/Mailgun/Hydrator/ModelHydrator.php
@@ -18,7 +18,7 @@ use Psr\Http\Message\ResponseInterface;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-class ModelHydrator implements Hydrator
+final class ModelHydrator implements Hydrator
 {
     /**
      * @param ResponseInterface $response
diff --git a/src/Mailgun/Hydrator/NoopHydrator.php b/src/Mailgun/Hydrator/NoopHydrator.php
index 478cd4d..f5d8c43 100644
--- a/src/Mailgun/Hydrator/NoopHydrator.php
+++ b/src/Mailgun/Hydrator/NoopHydrator.php
@@ -16,7 +16,7 @@ use Psr\Http\Message\ResponseInterface;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-class NoopHydrator implements Hydrator
+final class NoopHydrator implements Hydrator
 {
     /**
      * @param ResponseInterface $response
diff --git a/tests/Functional/MessageBuilderHeaderTest.php b/tests/Functional/MessageBuilderHeaderTest.php
index 0a61dd7..9d3fa33 100644
--- a/tests/Functional/MessageBuilderHeaderTest.php
+++ b/tests/Functional/MessageBuilderHeaderTest.php
@@ -23,7 +23,7 @@ class MessageBuilderHeaderTest extends \PHPUnit_Framework_TestCase
         };
 
         // Create the mocked mailgun client.
-        $mailgun = MockedMailgun::create($this, 'POST', 'domain/messages', [], $messageValidator);
+        $mailgun = MockedMailgun::createMock($this, 'POST', 'domain/messages', [], $messageValidator);
 
         $builder = $mailgun->MessageBuilder();