diff --git a/doc/source/firmware.rst b/doc/source/firmware.rst
index 5a3d4e81b13f43bf7ec4ba1fb673ea5333f690d5..37064a448c069c4ea693aade62a8cb196010cd61 100644
--- a/doc/source/firmware.rst
+++ b/doc/source/firmware.rst
@@ -443,8 +443,8 @@ like a regular command.
 | Transaction type: **Word write**
 | Data length: **2**
 
-Before writing a new FW binary through the bootloader, its size in
-bytes has to be given using this command.
+Before writing a new FW binary through the bootloader, its size in bytes
+divided by 8 has to be given using this command.
 
 .. _WRITTEN_FW_BLOCK: