diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index fc3b1c9e..832c570c 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -2101,10 +2101,6 @@ class SSH2
             return false;
         }
 
-        if (!is_string($password)) {
-            throw new \UnexpectedValueException('$password needs to either be an instance of \phpseclib\Crypt\Common\PrivateKey, \System\SSH\Agent, an array or a string');
-        }
-
         if (!isset($password)) {
            $packet = Strings::packSSH2(
                'Cs3',
@@ -2133,6 +2129,10 @@ class SSH2
             }
         }
 
+        if (!is_string($password)) {
+            throw new \UnexpectedValueException('$password needs to either be an instance of \phpseclib\Crypt\Common\PrivateKey, \System\SSH\Agent, an array or a string');
+        }
+
         $packet = Strings::packSSH2(
             'Cs3bs',
             NET_SSH2_MSG_USERAUTH_REQUEST,