diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index 6f9d5915..e2a219c7 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -3492,7 +3492,7 @@ class Math_BigInteger
                     break;
                 }
             }
-            $s = 26 * $i + $j - 1;
+            $s = 26 * $i + $j;
             $r->_rshift($s);
         }