diff --git a/reference/mcrypt/book.xml b/reference/mcrypt/book.xml
index 7929943e70..5e8e0568e6 100644
--- a/reference/mcrypt/book.xml
+++ b/reference/mcrypt/book.xml
@@ -15,6 +15,7 @@
    (default), 3-WAY, SAFER-SK64, SAFER-SK128, TWOFISH, TEA, RC2 and
    GOST in CBC, OFB, CFB and ECB cipher modes. Additionally, it
    supports RC6 and IDEA which are considered "non-free".
+   CFB/OFB are 8bit by default.
   </para>
  </preface>
  <!-- }}} -->