diff --git a/keystore/blob.h b/keystore/blob.h
index ce488ec..e0bd146 100644
--- a/keystore/blob.h
+++ b/keystore/blob.h
@@ -37,6 +37,7 @@
 constexpr size_t kGcmTagLength = 128 / 8;
 constexpr size_t kGcmIvLength = 96 / 8;
 constexpr size_t kAes128KeySizeBytes = 128 / 8;
+constexpr size_t kAes256KeySizeBytes = 256 / 8;
 
 /* Here is the file format. There are two parts in blob.value, the secret and
  * the description. The secret is stored in ciphertext, and its original size