diff --git a/phpseclib/Crypt/Random.php b/phpseclib/Crypt/Random.php
index 60884c5d..86ce6740 100644
--- a/phpseclib/Crypt/Random.php
+++ b/phpseclib/Crypt/Random.php
@@ -140,13 +140,13 @@ class Random
             session_start();
 
             $v = $seed = $_SESSION['seed'] = pack('H*', sha1(
-                serialize($_SERVER) .
-                serialize($_POST) .
-                serialize($_GET) .
-                serialize($_COOKIE) .
-                serialize($GLOBALS) .
-                serialize($_SESSION) .
-                serialize($_OLD_SESSION)
+                (isset($_SERVER) ? self::safe_serialize($_SERVER) : '') .
+                (isset($_POST) ? self::safe_serialize($_POST) : '') .
+                (isset($_GET) ? self::safe_serialize($_GET) : '') .
+                (isset($_COOKIE) ? self::safe_serialize($_COOKIE) : '') .
+                self::safe_serialize($GLOBALS) .
+                self::safe_serialize($_SESSION) .
+                self::safe_serialize($_OLD_SESSION)
             ));
             if (!isset($_SESSION['count'])) {
                 $_SESSION['count'] = 0;
@@ -232,4 +232,36 @@ class Random
         }
         return substr($result, 0, $length);
     }
+
+    /**
+     * Safely serialize variables
+     *
+     * If a class has a private __sleep() it'll emit a warning
+     *
+     * @param mixed $arr
+     * @access public
+     */
+    function safe_serialize(&$arr)
+    {
+        if (is_object($arr)) {
+            return '';
+        }
+        if (!is_array($arr)) {
+            return serialize($arr);
+        }
+        // prevent circular array recursion
+        if (isset($arr['__phpseclib_marker'])) {
+            return '';
+        }
+        $safearr = array();
+        $arr['__phpseclib_marker'] = true;
+        foreach (array_keys($arr) as $key) {
+            // do not recurse on the '__phpseclib_marker' key itself, for smaller memory usage
+            if ($key !== '__phpseclib_marker') {
+                $safearr[$key] = self::safe_serialize($arr[$key]);
+            }
+        }
+        unset($arr['__phpseclib_marker']);
+        return serialize($safearr);
+    }
 }