--- a/mercurial/commands.py	Wed Oct 12 21:45:58 2011 -0400
+++ b/mercurial/commands.py	Sat Oct 15 01:06:52 2011 +0200
@@ -4652,6 +4652,10 @@
         def badfn(path, msg):
             if path in names:
                 return
+            if path in repo[node].substate:
+                ui.warn("%s: %s\n" % (m.rel(path),
+                    'reverting subrepos is unsupported'))
+                return
             path_ = path + '/'
             for f in names:
                 if f.startswith(path_):