diff --git a/phpseclib/Crypt/Common/BlockCipher.php b/phpseclib/Crypt/Common/BlockCipher.php
index 2c685861..5f3abc98 100644
--- a/phpseclib/Crypt/Common/BlockCipher.php
+++ b/phpseclib/Crypt/Common/BlockCipher.php
@@ -23,4 +23,5 @@ namespace phpseclib3\Crypt\Common;
  */
 abstract class BlockCipher extends SymmetricKey
 {
+    public $mcrypt_polyfill_init;
 }