diff --git a/lisp/ox-html.el b/lisp/ox-html.el
index 319f178cb..5419ed50d 100644
--- a/lisp/ox-html.el
+++ b/lisp/ox-html.el
@@ -1279,7 +1279,7 @@ like that: \"%%\"."
 		(string :tag "Format string"))))
 
 (defcustom org-html-validation-link
-  "<a href=\"http://validator.w3.org/check?uri=referer\">Validate</a>"
+  "<a href=\"https://validator.w3.org/check?uri=referer\">Validate</a>"
   "Link to HTML validation service."
   :group 'org-export-html
   :type 'string)