diff --git a/pagure/lib/model.py b/pagure/lib/model.py
index d258c36..dc8ecbd 100644
--- a/pagure/lib/model.py
+++ b/pagure/lib/model.py
@@ -27,6 +27,7 @@ from sqlalchemy.orm import backref
 from sqlalchemy.orm import sessionmaker
 from sqlalchemy.orm import scoped_session
 from sqlalchemy.orm import relation
+from sqlalchemy.orm import validates
 
 
 CONVENTION = {
@@ -1709,7 +1710,7 @@ class PullRequestFlag(BASE):
         sa.String(64), sa.ForeignKey(
             'tokens.id',
         ),
-        nullable=False)
+        nullable=True)
     user_id = sa.Column(
         sa.Integer,
         sa.ForeignKey(
@@ -1747,6 +1748,11 @@ class PullRequestFlag(BASE):
         foreign_keys=[pull_request_uid],
         remote_side=[PullRequest.uid])
 
+    @validates('token_id')
+    def validate_token_id(self, _, token_id):
+        assert token_id is not None
+        return token_id
+
     def to_json(self, public=False):
         ''' Returns a dictionnary representation of the pull-request.
 
diff --git a/tests/test_pagure_lib.py b/tests/test_pagure_lib.py
index 42b0447..e5fae2a 100644
--- a/tests/test_pagure_lib.py
+++ b/tests/test_pagure_lib.py
@@ -2060,6 +2060,35 @@ class PagureLibtests(tests.Modeltests):
         self.assertEqual(len(request.flags), 1)
         self.assertEqual(request.flags[0].token_id, 'aaabbbcccddd')
 
+    @patch('pagure.lib.notify.send_email')
+    def test_add_pull_request_flag_no_token(self, mockemail):
+        """ Test add_pull_request_flag of pagure.lib. """
+        mockemail.return_value = True
+
+        self.test_new_pull_request()
+        tests.create_tokens(self.session)
+
+        request = pagure.lib.search_pull_requests(self.session, requestid=1)
+        self.assertEqual(len(request.flags), 0)
+
+        self.assertRaises(
+            AssertionError,
+            pagure.lib.add_pull_request_flag,
+            session=self.session,
+            request=request,
+            username="jenkins",
+            percent=100,
+            comment="Build passes",
+            url="http://jenkins.cloud.fedoraproject.org",
+            uid="jenkins_build_pagure_34",
+            user='foo',
+            token=None,
+            requestfolder=None,
+        )
+
+        request = pagure.lib.search_pull_requests(self.session, requestid=1)
+        self.assertEqual(len(request.flags), 0)
+
     def test_search_pull_requests(self):
         """ Test search_pull_requests of pagure.lib. """