diff --git a/phpseclib/Math/BigInteger/Engines/Engine.php b/phpseclib/Math/BigInteger/Engines/Engine.php
index 5d2dcaa8..3abdbc65 100644
--- a/phpseclib/Math/BigInteger/Engines/Engine.php
+++ b/phpseclib/Math/BigInteger/Engines/Engine.php
@@ -404,7 +404,7 @@ abstract class Engine implements \Serializable
         // (will always result in a smaller number.  ie. ~1 isn't 1111 1110 - it's 0)
         $temp = $this->toBytes();
         if ($temp == '') {
-            return '';
+            return $this->normalize(static::$zero);
         }
         $pre_msb = decbin(ord($temp[0]));
         $temp = ~$temp;