diff --git a/doc/PROTOCOL-WEB.md b/doc/PROTOCOL-WEB.md
index c3f9169b331b1d..99e473fef2304b 100644
--- a/doc/PROTOCOL-WEB.md
+++ b/doc/PROTOCOL-WEB.md
@@ -48,7 +48,8 @@ Content-Type
 HTTP wire protocols
 
 1. support any HTTP/*, with no dependency on HTTP/2 specific framing
-2. use lower-case header/trailer names
+2. use any casing for header/trailer names (following HTTP semantics, clients
+   must treat header and trailer names case-insensitively)
 3. use EOF (end of body) to close the stream
 
 ---