Use https:// URLs when referring to python.org hosts.
diff --git a/Doc/library/popen2.rst b/Doc/library/popen2.rst
index 628ec6e..0960255 100644
--- a/Doc/library/popen2.rst
+++ b/Doc/library/popen2.rst
@@ -153,7 +153,7 @@
 
 .. Example explanation and suggested work-arounds substantially stolen
    from Martin von Löwis:
-   http://mail.python.org/pipermail/python-dev/2000-September/009460.html
+   https://mail.python.org/pipermail/python-dev/2000-September/009460.html
 
 There are several ways to deal with this situation.