diff --git a/openslides/poll/serializers.py b/openslides/poll/serializers.py
index 82d4a6a6f..e9432537a 100644
--- a/openslides/poll/serializers.py
+++ b/openslides/poll/serializers.py
@@ -10,6 +10,8 @@ def default_votes_validator(data):
     than or equal to -2.
     """
     for key in data:
-        if key in ('votesvalid', 'votesinvalid', 'votescast') and data[key] < -2:
+        if (key in ('votesvalid', 'votesinvalid', 'votescast') and
+                data[key] is not None and
+                data[key] < -2):
             raise ValidationError({'detail': _('Value for {} must not be less than -2').format(key)})
     return data
diff --git a/tests/integration/assignments/test_viewset.py b/tests/integration/assignments/test_viewset.py
index 5c3ff649c..e209a23fe 100644
--- a/tests/integration/assignments/test_viewset.py
+++ b/tests/integration/assignments/test_viewset.py
@@ -307,3 +307,10 @@ class UpdateAssignmentPoll(TestCase):
             {'assignment_id': self.assignment.pk,
              'votescast': '-3'})
         self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+
+    def test_empty_value_for_votesvalid(self):
+        response = self.client.put(
+            reverse('assignmentpoll-detail', args=[self.poll.pk]),
+            {'assignment_id': self.assignment.pk,
+             'votesvalid': ''})
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
diff --git a/tests/integration/motions/test_viewset.py b/tests/integration/motions/test_viewset.py
index 81c14df24..aa02f9163 100644
--- a/tests/integration/motions/test_viewset.py
+++ b/tests/integration/motions/test_viewset.py
@@ -395,3 +395,10 @@ class UpdateMotionPoll(TestCase):
             {'motion_id': self.motion.pk,
              'votescast': '-3'})
         self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+
+    def test_empty_value_for_votesvalid(self):
+        response = self.client.put(
+            reverse('motionpoll-detail', args=[self.poll.pk]),
+            {'motion_id': self.motion.pk,
+             'votesvalid': ''})
+        self.assertEqual(response.status_code, status.HTTP_200_OK)