1 files changed, 5 insertions, 1 deletions

diff --git a/lisp/net/puny.el b/lisp/net/puny.el
index 5874871a90d..389a6dc2700 100644
--- a/lisp/net/puny.el
+++ b/lisp/net/puny.el
@@ -32,7 +32,11 @@
 (defun puny-encode-domain (domain)
   "Encode DOMAIN according to the IDNA/punycode algorith.
 For instance, \"fśf.org\" => \"xn--ff-2sa.org\"."
-  (mapconcat 'puny-encode-string (split-string domain "[.]") "."))
+  ;; The vast majority of domain names are not IDNA domain names, so
+  ;; add a check first to avoid doing unnecessary work.
+  (if (string-match "\\'[[:ascii:]]*\\'" domain)
+      domain
+    (mapconcat 'puny-encode-string (split-string domain "[.]") ".")))
 
 (defun puny-encode-string (string)
   "Encode STRING according to the IDNA/punycode algorithm.