diff --git a/composer.json b/composer.json
index fab85bd..b2a8d5e 100644
--- a/composer.json
+++ b/composer.json
@@ -40,11 +40,7 @@
   "autoload-dev": {
     "psr-4": {
       "SilverStripe\\BehatExtension\\Tests\\": "tests/php/"
-    },
-    "classmap": [
-      "framework",
-      "vendor/phpunit/phpunit"
-    ]
+    }
   },
   "extra": {
     "branch-alias": {
diff --git a/src/Compiler/CoreInitializationPass.php b/src/Compiler/CoreInitializationPass.php
index 390bab3..da785a4 100644
--- a/src/Compiler/CoreInitializationPass.php
+++ b/src/Compiler/CoreInitializationPass.php
@@ -7,6 +7,7 @@ use SilverStripe\Control\Controller;
 use SilverStripe\Control\HTTPApplication;
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Core\CoreKernel;
+use SilverStripe\Core\Environment;
 use SilverStripe\Core\Manifest\ModuleLoader;
 use SilverStripe\ORM\DataObject;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
@@ -28,8 +29,8 @@ class CoreInitializationPass implements CompilerPassInterface
         file_put_contents('php://stdout', 'Bootstrapping' . PHP_EOL);
 
         // Connect to database and build manifest
-        if (!getenv('SS_ENVIRONMENT_TYPE')) {
-            putenv('SS_ENVIRONMENT_TYPE=dev');
+        if (!Environment::getEnv('SS_ENVIRONMENT_TYPE')) {
+            Environment::setEnv('SS_ENVIRONMENT_TYPE', 'dev');
         }
 
         // Include bootstrap file
diff --git a/src/Compiler/MinkExtensionBaseUrlPass.php b/src/Compiler/MinkExtensionBaseUrlPass.php
index d26779d..1eceac2 100644
--- a/src/Compiler/MinkExtensionBaseUrlPass.php
+++ b/src/Compiler/MinkExtensionBaseUrlPass.php
@@ -3,6 +3,7 @@
 namespace SilverStripe\BehatExtension\Compiler;
 
 use InvalidArgumentException;
+use SilverStripe\Core\Environment;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
 
@@ -23,7 +24,7 @@ class MinkExtensionBaseUrlPass implements CompilerPassInterface
     public function process(ContainerBuilder $container)
     {
         // Set url from environment
-        $baseURL = getenv('SS_BASE_URL');
+        $baseURL = Environment::getEnv('SS_BASE_URL');
         if (!$baseURL) {
             throw new InvalidArgumentException(
                 '"base_url" not configured. Please specify it in your .env config with SS_BASE_URL'
diff --git a/src/Context/SilverStripeContext.php b/src/Context/SilverStripeContext.php
index 50b3033..6434906 100644
--- a/src/Context/SilverStripeContext.php
+++ b/src/Context/SilverStripeContext.php
@@ -10,8 +10,10 @@ use Behat\Mink\Driver\Selenium2Driver;
 use Behat\Mink\Exception\UnsupportedDriverActionException;
 use Behat\Mink\Exception\ElementNotFoundException;
 use InvalidArgumentException;
+use SilverStripe\BehatExtension\Utility\TestMailer;
 use SilverStripe\CMS\Model\SiteTree;
 use SilverStripe\Core\ClassInfo;
+use SilverStripe\Core\Environment;
 use SilverStripe\Core\Resettable;
 use SilverStripe\ORM\DataObject;
 use SilverStripe\TestSession\TestSessionEnvironment;
@@ -255,7 +257,7 @@ abstract class SilverStripeContext extends MinkContext implements SilverStripeAw
             $this->testSessionEnvironment->loadFixtureIntoDb($fixtureFile);
         }
 
-        if ($screenSize = getenv('BEHAT_SCREEN_SIZE')) {
+        if ($screenSize = Environment::getEnv('BEHAT_SCREEN_SIZE')) {
             list($screenWidth, $screenHeight) = explode('x', $screenSize);
             $this->getSession()->resizeWindow((int)$screenWidth, (int)$screenHeight);
         } else {
@@ -282,11 +284,11 @@ abstract class SilverStripeContext extends MinkContext implements SilverStripeAw
     public function getTestSessionState()
     {
         $extraParams = array();
-        parse_str(getenv('TESTSESSION_PARAMS'), $extraParams);
+        parse_str(Environment::getEnv('TESTSESSION_PARAMS'), $extraParams);
         return array_merge(
             array(
                 'database' => $this->databaseName,
-                'mailer' => 'SilverStripe\BehatExtension\Utility\TestMailer',
+                'mailer' => TestMailer::class,
             ),
             $extraParams
         );