diff --git a/swh/mirror/forge/sync.py b/swh/mirror/forge/sync.py
index 41584bf..c6516ec 100755
--- a/swh/mirror/forge/sync.py
+++ b/swh/mirror/forge/sync.py
@@ -1,132 +1,142 @@
 # Copyright (C) 2017  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import click
 import json
 import os
 import sys
 import requests
 
 from .api import RepositorySearch, PassphraseSearch, DiffusionUriEdit
 
 
 FORGE_API_URL = 'https://forge.softwareheritage.org'
 
 
 def load_token_from_file(filepath):
     """Loading the token."""
     with open(filepath, 'r') as f:
         return f.read().strip()
 
 
 def prepare_token():
     """Prepare the needed token from the disk.
 
     Returns:
         tuple (token-forge, token-github)
 
     """
     token_forge_filepath = os.getenv("HOME") + '/.config/swh/forge-token'
     token_forge = load_token_from_file(token_forge_filepath)
     if not token_forge:
         print("""Install the phabricator forge's token in %s
 (https://forge.softwareheritage.org/settings/user/<your-user>/page/apitokens/).
 
 Once the installation is done, you can trigger this script again.
         """ % token_forge_filepath)
         sys.exit(1)
 
     token_github_filepath = os.getenv("HOME") + '/.config/swh/github-token'
     token_github = load_token_from_file(token_github_filepath)
     if not token_github:
         print("""Install one personal github token in %s with scope
 public_repo (https://github.com/settings/tokens).
 
 You must be associated to https://github.com/softwareheritage
 organization.  Once the installation is done, you can trigger this
 script again.
         """ % token_github_filepath)
         sys.exit(1)
 
     return token_forge, token_github
 
 
 @click.command()
 @click.option('--repo-callsign',
               help="Repository's callsign")
 @click.option('--repo-name',
               help="Repository name (used in github)")
 @click.option('--repo-url',
               help="Repository's forge url (used in github)")
 @click.option('--repo-description',
               help="Repository's description (used in github)")
 @click.option('--credential-key-id',
               help="credential to use for access from phabricator's forge to github")
 @click.option('--github/--nogithub', default=True)
 def run(repo_callsign, repo_name, repo_url, repo_description,
         credential_key_id, github):
     """This will instantiate a mirror from a repository forge to github.
 
     """
     ### Retrieve credential access to github and phabricator's forge
     token_forge, token_github = prepare_token()
 
-    if github:
-        ### Create repository in github
+    ### Retrieve repository information
+
+    query = RepositorySearch(FORGE_API_URL, token_forge)
+    data = query.request(constraints={
+        "callsigns": [repo_callsign],
+    }, attachments={
+        "uris": True
+    })
+
+    repo_phid = data[0]['phid']
+
+    ### Check existence of mirror already set
+
+    for uri in data[0]['attachments']['uris']['uris']:
+        for url in uri['fields']['uri'].values():
+            if 'github' in url:
+                print('Mirror already installed at %s, stopping.' % url)
+                sys.exit(0)
+
+    ### Create repository in github
+    if github or mirror:
         r = requests.post(
             'https://api.github.com/orgs/SoftwareHeritage/repos',
             headers={'Authorization': 'token %s' % token_github},
             data=json.dumps({
                 "name": repo_name,
                 "description": repo_description,
                 "homepage": repo_url,
                 "private": False,
                 "has_issues": False,
                 "has_wiki": False,
                 "has_downloads": True
             }))
 
         if not r.ok:
             print("""Failure to create the repository in github.
 Status: %s""" % r.status_code)
             sys.exit(1)
 
-    ### Retrieve repository information
-
-    query = RepositorySearch(FORGE_API_URL, token_forge)
-    data = query.request(constraints={
-        "callsigns": [repo_callsign]
-    })
-
-    repo_phid = data[0]['phid']
-
     ### Retrieve credential information
 
     query = PassphraseSearch(FORGE_API_URL, token_forge)
     data = query.request(ids=[credential_key_id])
 
     # Retrieve the phid for that passphrase
     key_phid = list(data.values())[0]['phid']
 
     repo_url_github = 'git@github.com:SoftwareHeritage/%s.git' % repo_name
 
     ### Install the github mirror in the forge
 
     query = DiffusionUriEdit(FORGE_API_URL, token_forge)
     data = query.request(transactions=[
         {"type": "repository", "value": repo_phid},
         {"type": "uri", "value": repo_url_github},
         {"type": "io", "value": "mirror"},
         {"type": "display", "value": "never"},
         {"type": "disable", "value": False},
         {"type": "credential", "value": key_phid},
     ])
 
     print("Repository %s mirrored at %s." % (repo_url, repo_url_github))
     sys.exit(0)
 
 
 if __name__ == '__main__':
     run()