diff --git a/lisp/gnus/gnus-art.el b/lisp/gnus/gnus-art.el
index e9c2921a413..f36fdd29d62 100644
--- a/lisp/gnus/gnus-art.el
+++ b/lisp/gnus/gnus-art.el
@@ -7452,7 +7452,7 @@ groups."
   :group 'gnus-article-buttons
   :type 'regexp)
 
-(defcustom gnus-button-valid-fqdn-regexp "\\([-A-Za-z0-9]+\\.\\a)+[A-Za-z]+"
+(defcustom gnus-button-valid-fqdn-regexp "\\([-A-Za-z0-9]+\\.\\)+[A-Za-z]+"
   "Regular expression that matches a valid FQDN."
   :version "25.2"
   :group 'gnus-article-buttons