diff --git a/BSP.md b/BSP.md
index 8e7fe53..289cbc9 100644
--- a/BSP.md
+++ b/BSP.md
@@ -32,7 +32,9 @@ The channel descriptor is supplied by the client and is not interpreted by BSP.
 
 ### Message format
 
-Each message consists of one or more blocks. Each block is BLOCK_LEN bytes long, except the last block of the message, which may be shorter. (We require that BLOCK_LEN <= 2^15 .)
+Each message consists of one or more blocks. Each block is BLOCK_LEN bytes long, except the last block of the message, which may be shorter.
+
+> Implementation note: BLOCK_LEN must be ≤ 2^15 . We propose to use BLOCK_LEN = 2^15.
 
 * `message = block_1 || ... || block_n`