diff --git a/mercurial/httprepo.py b/mercurial/httprepo.py
--- a/mercurial/httprepo.py
+++ b/mercurial/httprepo.py
@@ -288,6 +288,7 @@ class httprepository(remoterepository):
         if not (proto.startswith('application/mercurial-') or
                 proto.startswith('text/plain') or
                 proto.startswith('application/hg-changegroup')):
+            self.ui.debug(_("Requested URL: '%s'\n") % cu)
             raise hg.RepoError(_("'%s' does not appear to be an hg repository")
                                % self._url)