diff --git a/specification/client_server_api.rst b/specification/client_server_api.rst
index 9e230334..9f942c94 100644
--- a/specification/client_server_api.rst
+++ b/specification/client_server_api.rst
@@ -362,6 +362,18 @@ Old V1 API docs: |register|_
 
 {{login_http_api}}
 
+Fallback
+++++++++
+
+If a client does not recognize any or all login flows it can use the fallback
+login API::
+
+    GET /_matrix/static/client/login/
+
+This returns an HTML and JavaScript page which can perform the entire login
+process. The page will attempt to call the JavaScript function
+``window.onLogin`` when login has been successfully completed.
+
 Changing Password
 +++++++++++++++++
 Request::