--- a/docs/mozreview/install-git.rst
+++ b/docs/mozreview/install-git.rst
@@ -125,16 +125,22 @@ Configuring a Repository to Submit to Mo
 ===============================================
 
 Each local Git repository wishing to submit patches to MozReview will
 need to be configured for MozReview integration. Configuring a
 repository is simple::
 
    $ git mozreview configure
 
+.. important::
+
+   MozReview only works with Git repository cloned from the Mercurial upstream.
+   `Documentation is available <https://github.com/glandium/git-cinnabar/wiki/Mozilla:-Using-a-git-clone-of-gecko%E2%80%90dev-to-push-to-mercurial#switching-to-git-cinnabar>`_
+   on how to switch a clone of ``gecko-dev`` mirror to ``hg.mozilla.org`` upstreams.
+
 If you manually configured global settings above, this command should
 complete automatically. If not, it will prompt you for e.g. your
 Bugzilla access credentials.
 
 By default, ``git mozreview configure`` will configure the ``review``
 Git remote. See ``git mozreview configure help`` on how to change the
 default remote name.
 

--- a/git/commands/git-mozreview
+++ b/git/commands/git-mozreview
@@ -608,16 +608,22 @@ def configure_command(args):
                                        git_config[key]])
                 git_config['mozreview.remote'] = git_config[key]
                 ui.warn('warning: will not need the "%s" remote anymore;\n'
                         'You may remove it with `git remote remove %s`.\n'
                         % (remote, remote))
 
     # Define the default remote url to use for pushing to MozReview.
     if 'mozreview.remote' not in git_config:
+        res, output = get_output(['git', 'for-each-ref', 'refs/cinnabar'])
+        if res or output == '':
+            raise AbortError('A non-cinnabar clone is detected; '
+                             'please clone the repository from the Mercurial upstream '
+                             'with git-cinnabar, instead of from a Git mirror.')
+
         ui.write('searching for appropriate review repository...\n')
         # Query the special "autoreview" repo for the list of review repos.
         url = '%s/autoreview/mozreviewreviewrepos' % args.mercurial_url
         res = requests.get(url)
         if res.status_code == 200:
             data = res.json()
             hg_shas = sorted(data.keys())
             res, output = get_output(['git', 'cinnabar', 'hg2git'] + hg_shas)