--- a/hgext3rd/topic/__init__.py	Mon Apr 16 10:58:06 2018 -0700
+++ b/hgext3rd/topic/__init__.py	Mon Apr 16 20:18:10 2018 +0200
@@ -594,10 +594,10 @@
         # Have some restrictions on the topic name just like bookmark name
         scmutil.checknewlabel(repo, topic, 'topic')
 
-        rmatch = re.match(br'[\w\-]+', topic)
+        rmatch = re.match(br'[-_.\w]+', topic)
         if not rmatch or rmatch.group(0) != topic:
             helptxt = _("topic names can only consist of alphanumeric, '-'"
-                        " and '_' characters")
+                        " '_' and '.' characters")
             raise error.Abort(_("invalid topic name: '%s'") % topic, hint=helptxt)
 
     compat.startpager(ui, 'topics')