diff --git a/rhodecode/controllers/admin/repos.py b/rhodecode/controllers/admin/repos.py
--- a/rhodecode/controllers/admin/repos.py
+++ b/rhodecode/controllers/admin/repos.py
@@ -120,8 +120,10 @@ class ReposController(BaseController):
 
         c.repos_list = [('', _('--REMOVE FORK--'))]
         c.repos_list += [(x.repo_id, x.repo_name) for x in
-                   Repository.query().order_by(Repository.repo_name).all()]
+                    Repository.query().order_by(Repository.repo_name).all()
+                    if x.repo_id != c.repo_info.repo_id]
 
+        defaults['id_fork_of'] = db_repo.fork.repo_id if db_repo.fork else ''
         return defaults
 
     @HasPermissionAllDecorator('hg.admin')
@@ -417,11 +419,11 @@ class ReposController(BaseController):
             repo = ScmModel().mark_as_fork(repo_name, fork_id,
                                     self.rhodecode_user.username)
             fork = repo.fork.repo_name if repo.fork else _('Nothing')
-            Session.commit()
-            h.flash(_('Marked repo %s as fork of %s') % (repo_name,fork),
+            Session().commit()
+            h.flash(_('Marked repo %s as fork of %s') % (repo_name, fork),
                     category='success')
         except Exception, e:
-            raise
+            log.error(traceback.format_exc())
             h.flash(_('An error occurred during this operation'),
                     category='error')
 
diff --git a/rhodecode/model/scm.py b/rhodecode/model/scm.py
--- a/rhodecode/model/scm.py
+++ b/rhodecode/model/scm.py
@@ -380,6 +380,8 @@ class ScmModel(BaseModel):
     def mark_as_fork(self, repo, fork, user):
         repo = self.__get_repo(repo)
         fork = self.__get_repo(fork)
+        if fork and repo.repo_id == fork.repo_id:
+            raise Exception("Cannot set repository as fork of itself")
         repo.fork = fork
         self.sa.add(repo)
         return repo
diff --git a/rhodecode/tests/__init__.py b/rhodecode/tests/__init__.py
--- a/rhodecode/tests/__init__.py
+++ b/rhodecode/tests/__init__.py
@@ -160,5 +160,5 @@ class TestController(TestCase):
         if not msg in response.session['flash'][0][1]:
             self.fail(
                 'msg `%s` not found in session flash: got `%s` instead' % (
-                      msg, response.session['flash'][0][1])
+                      msg, response.session['flash'])
             )
diff --git a/rhodecode/tests/functional/test_admin_settings.py b/rhodecode/tests/functional/test_admin_settings.py
--- a/rhodecode/tests/functional/test_admin_settings.py
+++ b/rhodecode/tests/functional/test_admin_settings.py
@@ -1,10 +1,11 @@
 # -*- coding: utf-8 -*-
 
 from rhodecode.lib.auth import get_crypt_password, check_password
-from rhodecode.model.db import User, RhodeCodeSetting
+from rhodecode.model.db import User, RhodeCodeSetting, Repository
 from rhodecode.tests import *
 from rhodecode.lib import helpers as h
 from rhodecode.model.user import UserModel
+from rhodecode.model.scm import ScmModel
 
 
 class TestAdminSettingsController(TestController):
@@ -211,3 +212,55 @@ class TestAdminSettingsController(TestCo
                                     old_data={})._messages['username_exists']
         msg = h.html_escape(msg % {'username': 'test_admin'})
         response.mustcontain(u"%s" % msg)
+
+    def test_set_repo_fork_has_no_self_id(self):
+        self.log_user()
+        repo = Repository.get_by_repo_name(HG_REPO)
+        response = self.app.get(url('edit_repo', repo_name=HG_REPO))
+        opt = """<option value="%s">vcs_test_git</option>""" % repo.repo_id
+        assert opt not in response.body
+
+    def test_set_fork_of_repo(self):
+        self.log_user()
+        repo = Repository.get_by_repo_name(HG_REPO)
+        repo2 = Repository.get_by_repo_name(GIT_REPO)
+        response = self.app.put(url('repo_as_fork', repo_name=HG_REPO),
+                                 params=dict(
+                                    id_fork_of=repo2.repo_id
+                                 ))
+        repo = Repository.get_by_repo_name(HG_REPO)
+        repo2 = Repository.get_by_repo_name(GIT_REPO)
+        self.checkSessionFlash(response,
+        'Marked repo %s as fork of %s' % (repo.repo_name, repo2.repo_name))
+
+        assert repo.fork == repo2
+        response = response.follow()
+        # check if given repo is selected
+
+        opt = """<option value="%s" selected="selected">%s</option>""" % (
+                                                repo2.repo_id, repo2.repo_name)
+        response.mustcontain(opt)
+
+        # clean session flash
+        #response = self.app.get(url('edit_repo', repo_name=HG_REPO))
+
+        ## mark it as None
+        response = self.app.put(url('repo_as_fork', repo_name=HG_REPO),
+                                 params=dict(
+                                    id_fork_of=None
+                                 ))
+        repo = Repository.get_by_repo_name(HG_REPO)
+        repo2 = Repository.get_by_repo_name(GIT_REPO)
+        self.checkSessionFlash(response,
+        'Marked repo %s as fork of %s' % (repo.repo_name, "Nothing"))
+        assert repo.fork == None
+
+    def test_set_fork_of_same_repo(self):
+        self.log_user()
+        repo = Repository.get_by_repo_name(HG_REPO)
+        response = self.app.put(url('repo_as_fork', repo_name=HG_REPO),
+                                 params=dict(
+                                    id_fork_of=repo.repo_id
+                                 ))
+        self.checkSessionFlash(response,
+                               'An error occurred during this operation')
\ No newline at end of file