diff --git a/lib/src/bip39_base.dart b/lib/src/bip39_base.dart
index 6b0d61e..b30429f 100644
--- a/lib/src/bip39_base.dart
+++ b/lib/src/bip39_base.dart
@@ -7,7 +7,7 @@ import 'package:hex/hex.dart';
 import 'utils/pbkdf2.dart';
 import 'wordlists/english.dart';
 
-const int _SIZE_BYTE = 255;
+const int _SIZE_BYTE = 256;
 const _INVALID_MNEMONIC = 'Invalid mnemonic';
 const _INVALID_ENTROPY = 'Invalid entropy';
 const _INVALID_CHECKSUM = 'Invalid mnemonic checksum';