diff --git a/Doc/library/cgi.rst b/Doc/library/cgi.rst
index c151f04dfb8..a2957ba5a68 100644
--- a/Doc/library/cgi.rst
+++ b/Doc/library/cgi.rst
@@ -21,6 +21,11 @@ Support module for Common Gateway Interface (CGI) scripts.
 This module defines a number of utilities for use by CGI scripts written in
 Python.
 
+The global variable ``maxlen`` can be set to an integer indicating the maximum
+size of a POST request. POST requests larger than this size will result in a
+:exc:`ValueError` being raised during parsing. The default value of this
+variable is ``0``, meaning the request size is unlimited.
+
 
 Introduction
 ------------
diff --git a/Lib/cgi.py b/Lib/cgi.py
index 6cb8cf28bd6..22897a14a9c 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -13,6 +13,11 @@
 
 This module defines a number of utilities for use by CGI scripts
 written in Python.
+
+The global variable maxlen can be set to an integer indicating the maximum size
+of a POST request. POST requests larger than this size will result in a
+ValueError being raised during parsing. The default value of this variable is 0,
+meaning the request size is unlimited.
 """
 
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