diff --git a/openslides/assignment/forms.py b/openslides/assignment/forms.py
index 1062c4888..f8423e1d7 100644
--- a/openslides/assignment/forms.py
+++ b/openslides/assignment/forms.py
@@ -20,6 +20,7 @@ from assignment.models import Assignment
 
 
 class AssignmentForm(ModelForm, CssClassMixin):
+    posts = forms.IntegerField(min_value=1)
     class Meta:
         model = Assignment
         exclude = ('status', 'profile', 'elected')