diff --git a/runtime/doc/if_pyth.txt b/runtime/doc/if_pyth.txt
index 572e6bf..79b1716 100644
--- a/runtime/doc/if_pyth.txt
+++ b/runtime/doc/if_pyth.txt
@@ -1,4 +1,4 @@
-*if_pyth.txt*   For Vim version 8.2.  Last change: 2019 Dec 07
+*if_pyth.txt*   For Vim version 8.2.  Last change: 2021 Nov 12
 
 
 		  VIM REFERENCE MANUAL    by Paul Moore
@@ -63,6 +63,11 @@
 
 There is no need to import sys, it's done by default.
 
+							*python-environment*
+Environment variables set in Vim are not always available in Python.  This
+depends on how Vim and Python were build.  Also see
+https://docs.python.org/3/library/os.html#os.environ
+
 Note: Python is very sensitive to the indenting.  Make sure the "class" line
 and "EOF" do not have any indent.