Index: django/db/models/fields/__init__.py
===================================================================
--- django/db/models/fields/__init__.py (revision 6194)
+++ django/db/models/fields/__init__.py (working copy)
@@ -910,11 +910,21 @@
 class PositiveIntegerField(IntegerField):
     def get_manipulator_field_objs(self):
         return [oldforms.PositiveIntegerField]
+    
+    def formfield(self, **kwargs):
+        defaults = {'min_value': 0}
+        defaults.update(kwargs)
+        return super(PositiveIntegerField, self).formfield(**defaults) 
 
 class PositiveSmallIntegerField(IntegerField):
     def get_manipulator_field_objs(self):
         return [oldforms.PositiveSmallIntegerField]
 
+    def formfield(self, **kwargs):
+        defaults = {'min_value': 0}
+        defaults.update(kwargs)
+        return super(PositiveSmallIntegerField, self).formfield(**defaults) 
+
 class SlugField(CharField):
     def __init__(self, *args, **kwargs):
         kwargs['max_length'] = kwargs.get('max_length', 50)