diff --git a/gluon/tests/test_validators.py b/gluon/tests/test_validators.py
index 77a7e6b5..e534fbd8 100644
--- a/gluon/tests/test_validators.py
+++ b/gluon/tests/test_validators.py
@@ -235,6 +235,11 @@ class TestValidators(unittest.TestCase):
         self.assertEqual(sorted(rtn), [('%d' % george_id, 'george'), ('%d' % costanza_id, 'costanza')])
         rtn = IS_IN_DB(db, db.person.id, db.person.name, error_message='oops', sort=True).options(zero=True)
         self.assertEqual(rtn, [('', ''), ('%d' % costanza_id, 'costanza'), ('%d' % george_id, 'george')])
+        # Test None
+        rtn = IS_IN_DB(db, 'person.id', '%(name)s', error_message='oops')(None)
+        self.assertEqual(rtn, (None, 'oops'))
+        rtn = IS_IN_DB(db, 'person.name', '%(name)s', error_message='oops')(None)
+        self.assertEqual(rtn, (None, 'oops'))
         # Test using the set it made for options
         vldtr = IS_IN_DB(db, 'person.name', '%(name)s', error_message='oops')
         vldtr.options()
diff --git a/gluon/validators.py b/gluon/validators.py
index 7ace3c5c..90ee8302 100644
--- a/gluon/validators.py
+++ b/gluon/validators.py
@@ -21,7 +21,7 @@ import urllib
 import struct
 import decimal
 import unicodedata
-from gluon._compat import StringIO, long, basestring, unicodeT, to_unicode, urllib_unquote, unichr, to_bytes, PY2, to_unicode, to_native
+from gluon._compat import StringIO, long, basestring, unicodeT, to_unicode, urllib_unquote, unichr, to_bytes, PY2, to_unicode, to_native, string_types
 from gluon.utils import simple_hash, web2py_uuid, DIGEST_ALG_BY_SIZE
 from pydal.objects import Field, FieldVirtual, FieldMethod
 from functools import reduce
@@ -659,7 +659,7 @@ class IS_IN_DB(Validator):
                     return (values, None)
         else:
             if field.type in ('id', 'integer'):
-                if isinstance(value, (int, long)) or value.isdigit():
+                if isinstance(value, (int, long)) or (isinstance(value, string_types) and value.isdigit()):
                     value = int(value)
                 elif self.auto_add:
                     value = self.maybe_add(table, self.fieldnames[0], value)