Index: tests/modeltests/model_forms/models.py
===================================================================
--- tests/modeltests/model_forms/models.py      (revision 6194)
+++ tests/modeltests/model_forms/models.py      (working copy)
@@ -70,6 +70,9 @@
     def __unicode__(self):
         return self.phone
 
+class BoundaryModel(models.Model):
+    positive_integer = models.PositiveIntegerField(null=True, blank=True)
+
 __test__ = {'API_TESTS': """
 >>> from django.newforms import form_for_model, form_for_instance, save_instance, BaseForm, Form, CharField
 >>> import datetime
@@ -560,4 +563,13 @@
 True
 >>> f.cleaned_data
 {'phone': u'312-555-1212', 'description': u'Assistance'}
+
+# Boundary conditions / validation ############################################
+>>> BoundaryForm = form_for_model(BoundaryModel)
+>>> f = BoundaryForm({'positive_integer':100})
+>>> f.is_valid()
+True
+>>> f = BoundaryForm({'positive_integer':-100})
+>>> f.is_valid()
+False