diff --git a/doc/Guidebook.mn b/doc/Guidebook.mn
index 7b841ebe4..4c4cd5f11 100644
--- a/doc/Guidebook.mn
+++ b/doc/Guidebook.mn
@@ -5151,7 +5151,7 @@ fixes to NetHack 3.6.2.
 .pg
 The official NetHack web site is maintained by \fBKen Lorber\fP
 at
-.UR http://www.nethack.org/ .
+.UR https://www.nethack.org/ .
 .pg
 .hn 2
 SPECIAL THANKS
diff --git a/doc/Guidebook.tex b/doc/Guidebook.tex
index 5d6280b56..049aa8598 100644
--- a/doc/Guidebook.tex
+++ b/doc/Guidebook.tex
@@ -5757,8 +5757,8 @@ fixes to NetHack 3.6.2.
 \medskip
 \nd The official {\it NetHack\/} web site is maintained by {\it Ken Lorber} at
 {\catcode`\#=11
-\special{html:<a href="http://www.nethack.org/">}}
-http:{\tt /}{\tt /}www.nethack.org{\tt /}.
+\special{html:<a href="https://www.nethack.org/">}}
+https:{\tt /}{\tt /}www.nethack.org{\tt /}.
 {\catcode`\#=11
 \special{html:</a>}}