--- a/hgext3rd/topic/__init__.py	Tue Aug 23 21:18:47 2016 +0200
+++ b/hgext3rd/topic/__init__.py	Fri Aug 26 12:37:52 2016 +0200
@@ -196,6 +196,10 @@
     if list:
         if clear or change:
             raise error.Abort(_("cannot use --clear or --change with --list"))
+        if not topic:
+            topic = repo.currenttopic
+        if not topic:
+            raise error.Abort(_('no active topic to list'))
         return stack.showstack(ui, repo, topic, opts)
 
     if change:
@@ -275,6 +279,10 @@
     """list all changesets in a topic
 
     List the current topic by default."""
+    if not topic:
+        topic = repo.currenttopic
+    if not topic:
+        raise error.Abort(_('no active topic to list'))
     return stack.showstack(ui, repo, topic, opts)
 
 def _listtopics(ui, repo, opts):