diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index a8501ab8639..3823981b37c 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -547,7 +547,8 @@ request.
    name, and later calls will overwrite previous calls in case the *key* collides.
    Currently, this is no loss of HTTP functionality, since all headers which have
    meaning when used more than once have a (header-specific) way of gaining the
-   same functionality using only one header.
+   same functionality using only one header.  Note that headers added using
+   this method are also added to redirected requests.
 
 
 .. method:: Request.add_unredirected_header(key, header)