diff --git a/src/Message/ServerRequest.php b/src/Message/ServerRequest.php
index 601499f..6ec61aa 100644
--- a/src/Message/ServerRequest.php
+++ b/src/Message/ServerRequest.php
@@ -4,7 +4,9 @@ namespace WellRESTed\Message;
 
 use InvalidArgumentException;
 use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Message\StreamInterface;
 use Psr\Http\Message\UploadedFileInterface;
+use Psr\Http\Message\UriInterface;
 
 /**
  * Representation of an incoming, server-side HTTP request.
@@ -51,9 +53,31 @@ class ServerRequest extends Request implements ServerRequestInterface
 
     // -------------------------------------------------------------------------
 
-    public function __construct(array $serverParams = [])
-    {
-        parent::__construct();
+    /**
+     * Create a new ServerRequest.
+     *
+     * $headers is an optional associative array with header field names as
+     * string keys and values as either string or string[].
+     *
+     * If no StreamInterface is provided for $body, the instance will create
+     * a NullStream instance for the message body.
+     *
+     * @param string $method
+     * @param string|UriInterface $uri
+     * @param array $headers Associative array with header field names as
+     *     keys and values as string|string[]
+     * @param StreamInterface|null $body A stream representation of the message
+     *     entity body
+     * @param array $serverParams An array of Server API (SAPI) parameters
+     */
+    public function __construct(
+        string $method = 'GET',
+        $uri = '',
+        array $headers = [],
+        ?StreamInterface $body = null,
+        array $serverParams = []
+    ){
+        parent::__construct($method, $uri, $headers, $body);
         $this->serverParams = $serverParams;
         $this->cookieParams = [];
         $this->queryParams = [];
diff --git a/src/Message/ServerRequestMarshaller.php b/src/Message/ServerRequestMarshaller.php
index 9b67065..ae61317 100644
--- a/src/Message/ServerRequestMarshaller.php
+++ b/src/Message/ServerRequestMarshaller.php
@@ -8,38 +8,28 @@ use Psr\Http\Message\UriInterface;
 
 class ServerRequestMarshaller
 {
-    public function getServerRequest(
-        ?array $serverParams = null,
-        ?array $cookieParams = null,
-        ?array $queryParams = null,
-        ?array $postParams = null,
-        ?array $fileParams = null,
-        string $inputStream = 'php://input'
-    ): ServerRequestInterface {
-        $serverParams = $serverParams ?? $_SERVER;
-        $cookieParams = $cookieParams ?? $_COOKIE;
-        $queryParams = $queryParams ?? self::parseQuery($serverParams);
-        $postParams = $postParams ?? $_POST;
-        $fileParams = $fileParams ?? $_FILES;
+    /**
+     * Read the request as sent from the client and construct a ServerRequest
+     * representation.
+     *
+     * @return ServerRequestInterface
+     * @internal
+     */
+    public function getServerRequest(): ServerRequestInterface
+    {
+        $method = self::parseMethod($_SERVER);
+        $uri = self::readUri($_SERVER);
+        $headers = self::parseHeaders($_SERVER);
+        $body = self::readBody();
 
-        $request = new ServerRequest($serverParams);
-
-        $request = $request
-            ->withProtocolVersion(self::parseProtocolVersion($serverParams))
-            ->withMethod(self::parseMethod($serverParams))
-            ->withBody(self::readBody($inputStream))
-            ->withUri(self::readUri($serverParams))
-            ->withUploadedFiles(self::readUploadedFiles($fileParams))
-            ->withCookieParams($cookieParams)
-            ->withQueryParams($queryParams);
-
-        $headers = self::parseHeaders($serverParams);
-        foreach ($headers as $name => $value) {
-            $request = $request->withAddedHeader($name, $value);
-        }
+        $request = (new ServerRequest($method, $uri, $headers, $body, $_SERVER))
+            ->withProtocolVersion(self::parseProtocolVersion($_SERVER))
+            ->withUploadedFiles(self::readUploadedFiles($_FILES))
+            ->withCookieParams($_COOKIE)
+            ->withQueryParams(self::parseQuery($_SERVER));
 
         if (self::isForm($request)) {
-            $request = $request->withParsedBody($postParams);
+            $request = $request->withParsedBody($_POST);
         }
 
         return $request;
@@ -95,9 +85,9 @@ class ServerRequestMarshaller
         return $serverParams['REQUEST_METHOD'] ?? 'GET';
     }
 
-    private static function readBody(string $inputStream): StreamInterface
+    private static function readBody(): StreamInterface
     {
-        $input = fopen($inputStream, 'rb');
+        $input = fopen('php://input', 'rb');
         $temp = fopen('php://temp', 'wb+');
         stream_copy_to_stream($input, $temp);
         rewind($temp);
diff --git a/tests/Message/ServerRequestMarshallerTest.php b/tests/Message/ServerRequestMarshallerTest.php
index c579371..1bf829f 100644
--- a/tests/Message/ServerRequestMarshallerTest.php
+++ b/tests/Message/ServerRequestMarshallerTest.php
@@ -28,6 +28,8 @@ class ServerRequestMarshallerTest extends TestCase
             'hamster' => 'Dusty'
         ];
 
+        FopenHelper::$inputTempFile = null;
+
         $this->marshaller = new ServerRequestMarshaller();
     }
 
@@ -103,15 +105,9 @@ class ServerRequestMarshallerTest extends TestCase
         $tempFilePath = tempnam(sys_get_temp_dir(), 'test');
         $content = 'Body content';
         file_put_contents($tempFilePath, $content);
+        FopenHelper::$inputTempFile = $tempFilePath;
 
-        $request = $this->marshaller->getServerRequest(
-            null,
-            null,
-            null,
-            null,
-            null,
-            $tempFilePath
-        );
+        $request = $this->marshaller->getServerRequest();
         unlink($tempFilePath);
 
         $this->assertEquals($content, (string) $request->getBody());
@@ -182,7 +178,8 @@ class ServerRequestMarshallerTest extends TestCase
      */
     public function testProvidesUri(UriInterface $expected, array $serverParams): void
     {
-        $request = $this->marshaller->getServerRequest($serverParams);
+        $_SERVER = $serverParams;
+        $request = $this->marshaller->getServerRequest();
         $this->assertEquals($expected, $request->getUri());
     }
 
@@ -379,3 +376,25 @@ class ServerRequestMarshallerTest extends TestCase
         ];
     }
 }
+
+// -----------------------------------------------------------------------------
+
+// Declare fopen function in this namespace so the class under test will use
+// this instead of the internal global functions during testing.
+
+class FopenHelper
+{
+    /**
+     * @var string Path to temp file to read in place of 'php://input'
+     */
+    public static $inputTempFile;
+}
+
+function fopen($filename, $mode)
+{
+    if (FopenHelper::$inputTempFile && $filename === 'php://input') {
+        $filename = FopenHelper::$inputTempFile;
+    }
+
+    return \fopen($filename, $mode);
+}