diff --git a/doc/sources/nghttpx-howto.rst b/doc/sources/nghttpx-howto.rst
index e7549de8..7c56984a 100644
--- a/doc/sources/nghttpx-howto.rst
+++ b/doc/sources/nghttpx-howto.rst
@@ -435,6 +435,15 @@ such PSK cipher suite with HTTP/2, disable HTTP/2 cipher black list by
 using :option:`--client-no-http2-cipher-black-list` option.  But you
 should understand its implications.
 
+Migration from nghttpx v1.21.x or earlier
+-----------------------------------------
+
+As of nghttpx v1.22.0, it does not strip and append X-Forwarded-Proto
+header field by default.  In order to recover the previous behaviour,
+that is always strip incoming X-Forwarded-Proto and append its own,
+use :option:`--add-x-forwarded-proto` and
+:option:`--strip-incoming-x-forwarded-proto` options.
+
 Migration from nghttpx v1.18.x or earlier
 -----------------------------------------