diff --git a/qemu-options.hx b/qemu-options.hx
index f7c83362d1..aec2328736 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3100,6 +3100,8 @@ SRST
         server. The files in dir will be exposed as the root of a TFTP
         server. The TFTP client on the guest must be configured in
         binary mode (use the command ``bin`` of the Unix TFTP client).
+        The built-in TFTP server is read-only; it does not implement any
+        command for writing files. QEMU will not write to this directory.
 
     ``tftp-server-name=name``
         In BOOTP reply, broadcast name as the "TFTP server name"