diff --git a/docs/ref/request-response.txt b/docs/ref/request-response.txt
index fbc83bc379..86a9a02172 100644
--- a/docs/ref/request-response.txt
+++ b/docs/ref/request-response.txt
@@ -153,6 +153,12 @@ All attributes should be considered read-only, unless stated otherwise below.
     header called ``X-Bender`` would be mapped to the ``META`` key
     ``HTTP_X_BENDER``.
 
+    Note that :djadmin:`runserver` strips all headers with underscores in the
+    name, so you won't see them in ``META``. This prevents header-spoofing
+    based on ambiguity between underscores and dashes both being normalizing to
+    underscores in WSGI environment variables. It matches the behavior of
+    Web servers like Nginx and Apache 2.4+.
+
 .. attribute:: HttpRequest.user
 
     An object of type :setting:`AUTH_USER_MODEL` representing the currently