diff --git a/tests/PHPCurlClass/ContentRangeServer.php b/tests/PHPCurlClass/ContentRangeServer.php
index 796d2c1..8e6e6d5 100644
--- a/tests/PHPCurlClass/ContentRangeServer.php
+++ b/tests/PHPCurlClass/ContentRangeServer.php
@@ -8,8 +8,6 @@ class ContentRangeServer
 {
     public function serve($path)
     {
-        $range = new RangeHeader($_SERVER['HTTP_RANGE']);
-
         $filesize = filesize($path);
         $fp = fopen($path, 'r');
 
@@ -19,16 +17,25 @@ class ContentRangeServer
             header('Accept-Ranges: bytes');
             fpassthru($fp);
         } else {
-            header('HTTP/1.1 206 Partial Content');
-            header('Content-Length: ' . $range->getLength($filesize));
-            header('Content-Range: ' . $range->getContentRangeHeader($filesize));
+            $range = new RangeHeader($_SERVER['HTTP_RANGE'], $path);
 
-            $start = $range->getFirstBytePosition($filesize);
+            if (!$range->isValid()) {
+                header('HTTP/1.1 416 Requested Range Not Satisfiable');
+                header('Content-Range: ' . $range->getContentRangeHeader());
+                exit;
+            }
+
+            $length = $range->getLength();
+
+            header('HTTP/1.1 206 Partial Content');
+            header('Content-Length: ' . $length);
+            header('Content-Range: ' . $range->getContentRangeHeader());
+
+            $start = $range->getFirstBytePosition();
             if ($start > 0) {
                 fseek($fp, $start, SEEK_SET);
             }
 
-            $length = $range->getLength($filesize);
             $chunk_size = 4096;
             while ($length) {
                 $read = $length > $chunk_size ? $chunk_size : $length;
diff --git a/tests/PHPCurlClass/RangeHeader.php b/tests/PHPCurlClass/RangeHeader.php
index ff0c1cf..3835e15 100644
--- a/tests/PHPCurlClass/RangeHeader.php
+++ b/tests/PHPCurlClass/RangeHeader.php
@@ -6,48 +6,65 @@ class RangeHeader
 {
     private $first_byte;
     private $last_byte;
+    private $filesize;
+    private $is_valid = true;
 
-    public function __construct($http_range_header)
+    public function __construct($http_range_header, $file_path)
     {
         // Simulate basic support for the Content-Range header.
         preg_match('/bytes=(\d+)?-(\d+)?/', $http_range_header, $matches);
         $this->first_byte = isset($matches['1']) ? (int)$matches['1'] : null;
         $this->last_byte = isset($matches['2']) ? (int)$matches['2'] : null;
+
+        $this->filesize = filesize($file_path);
+
+        // Start position begins after end of file.
+        if ($this->first_byte >= $this->filesize) {
+            $this->is_valid = false;
+        }
+
+        // "If the last-byte-pos value is present, it MUST be greater than or equal to the first-byte-pos in that
+        // byte-range-spec, or the byte- range-spec is syntactically invalid."
+        if (!($this->last_byte === null) && !($this->last_byte >= $this->first_byte)) {
+            $this->is_valid = false;
+        }
     }
 
-    public function getFirstBytePosition($file_size)
+    public function getFirstBytePosition()
     {
-        $size = (int)$file_size;
-
         if ($this->first_byte === null) {
-            return $size - 1 - $this->last_byte;
+            return $this->filesize - 1 - $this->last_byte;
         }
 
         return $this->first_byte;
     }
 
-    public function getLastBytePosition($file_size)
+    public function getLastBytePosition()
     {
-        $size = (int)$file_size;
-
         if ($this->last_byte === null) {
-            return $size - 1;
+            return $this->filesize - 1;
         }
 
         return $this->last_byte;
     }
 
-    public function getLength($file_size)
+    public function getLength()
     {
-        $size = (int)$file_size;
-
-        return $this->getLastBytePosition($size) - $this->getFirstBytePosition($size) + 1;
+        return $this->getLastBytePosition() - $this->getFirstBytePosition() + 1;
     }
 
-    public function getContentRangeHeader($file_size)
+    public function getByteRangeSpec()
     {
-        return
-            'bytes ' . $this->getFirstBytePosition($file_size) . '-' . $this->getLastBytePosition($file_size) . '/' .
-            $file_size;
+        return $this->is_valid ? $this->getFirstBytePosition() . '-' . $this->getLastBytePosition() : '*';
+    }
+
+    public function getContentRangeHeader()
+    {
+        return 'bytes ' . $this->getByteRangeSpec() . '/' .  $this->filesize;
+    }
+
+    public function isValid()
+    {
+        return $this->is_valid;
     }
 }