diff --git a/.travis.yml b/.travis.yml
index 8c71a48..84c7bac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,6 @@
 language: php
 
 php:
-  - 5.5
   - 5.6
   - 7.0
   - 7.1
diff --git a/composer.json b/composer.json
index 2f1b50f..a66bf6c 100644
--- a/composer.json
+++ b/composer.json
@@ -10,11 +10,13 @@
         "maintenance"
     ],
     "require": {
-        "php": ">=5.5",
-        "psr/http-message": "^1.0"
+        "php": ">=5.6",
+        "psr/http-message": "^1.0",
+        "php-middleware/double-pass-compatibility": "^1.0",
+        "http-interop/http-middleware": "^0.4.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.6",
+        "phpunit/phpunit": "^5.6 || ^6.1",
         "zendframework/zend-diactoros": "^1.1.3"
     },
     "autoload": {
diff --git a/src/MaintenanceMiddleware.php b/src/MaintenanceMiddleware.php
index d38925d..c403de1 100644
--- a/src/MaintenanceMiddleware.php
+++ b/src/MaintenanceMiddleware.php
@@ -2,11 +2,19 @@
 
 namespace PhpMiddleware\Maintenance;
 
-use Psr\Http\Message\ResponseInterface;
+use DateTime;
+use DateTimeInterface;
+use Interop\Http\ServerMiddleware\DelegateInterface;
+use Interop\Http\ServerMiddleware\MiddlewareInterface;
+use InvalidArgumentException;
+use PhpMiddleware\DoublePassCompatibilityTrait;
 use Psr\Http\Message\ServerRequestInterface;
+use Zend\Diactoros\Response;
 
-final class MaintenanceMiddleware
+final class MaintenanceMiddleware implements MiddlewareInterface
 {
+    use DoublePassCompatibilityTrait;
+
     /**
      * @var string
      */
@@ -22,7 +30,7 @@ private function __construct()
     }
 
     /**
-     * @return \self
+     * @return self
      */
     public static function create()
     {
@@ -37,7 +45,7 @@ public static function create()
     public static function createWithRetryAsSeconds($seconds)
     {
         if (!is_int($seconds)) {
-            throw new \InvalidArgumentException('Seconds must be integer');
+            throw new InvalidArgumentException('Seconds must be integer');
         }
         $instance = new self();
         $instance->retryAfter = (string) $seconds;
@@ -59,25 +67,25 @@ public static function createWithRetryAsSecondsAndRefresh($seconds)
     }
 
     /**
-     * @param \DateTimeInterface $datetime
+     * @param DateTimeInterface $datetime
      *
      * @return self
      */
-    public static function createWithRetryAsDateTime(\DateTimeInterface $datetime)
+    public static function createWithRetryAsDateTime(DateTimeInterface $datetime)
     {
         $instance = new self();
 
-        $instance->retryAfter = $datetime->format(\DateTime::RFC2822);
+        $instance->retryAfter = $datetime->format(DateTime::RFC2822);
 
         return $instance;
     }
 
     /**
-     * @param \DateTimeInterface $datetime
+     * @param DateTimeInterface $datetime
      *
      * @return self
      */
-    public static function createWithRetryAsDateTimeAndRefresh(\DateTimeInterface $datetime)
+    public static function createWithRetryAsDateTimeAndRefresh(DateTimeInterface $datetime)
     {
         $instance = self::createWithRetryAsDateTime($datetime);
         $diff = time() - $datetime->getTimestamp();
@@ -86,23 +94,19 @@ public static function createWithRetryAsDateTimeAndRefresh(\DateTimeInterface $d
         return $instance;
     }
 
-    /**
-     * @param ServerRequestInterface $request
-     * @param ResponseInterface $response
-     * @param callable $next
-     *
-     * @return ResponseInterface
-     */
-    public function __invoke(ServerRequestInterface $request, ResponseInterface $response, callable $next)
+    public function process(ServerRequestInterface $request, DelegateInterface $delegate)
     {
+        $headers = [];
+
         if ($this->retryAfter !== '') {
-            $response = $response->withHeader('Retry-After', $this->retryAfter);
+            $headers['Retry-After'] = $this->retryAfter;
 
             if ($this->refresh > 0) {
-                $response = $response->withHeader('Refresh', (string) $this->refresh);
+                $headers['Refresh'] = (string) $this->refresh;
             }
         }
 
-        return $response->withStatus(503);
+        return new Response('php://memory', 503, $headers);
     }
+
 }
diff --git a/test/MaintenanceMiddlewareTest.php b/test/MaintenanceMiddlewareTest.php
index 25930e8..6375ba4 100644
--- a/test/MaintenanceMiddlewareTest.php
+++ b/test/MaintenanceMiddlewareTest.php
@@ -5,11 +5,11 @@
 use DateTime;
 use Exception;
 use PhpMiddleware\Maintenance\MaintenanceMiddleware;
-use PHPUnit_Framework_TestCase;
+use PHPUnit\Framework\TestCase;
 use Zend\Diactoros\Response;
 use Zend\Diactoros\ServerRequest;
 
-class MaintenanceMiddlewareTest extends PHPUnit_Framework_TestCase
+class MaintenanceMiddlewareTest extends TestCase
 {
     public function testWithoutRetry()
     {