diff --git a/CHANGES.rst b/CHANGES.rst
index c961a88..5dbc02a 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -12,7 +12,7 @@ master (unreleased)
   ``update_fields`` in which there are untracked fields. Thanks Mikhail
   Silonov. (Merge of GH-70, fixes GH-71).
 
-* Added JSON Fields support.
+* Added support for mutable fields (Merge of GH-73, fixes GH-74)
 
 
 1.4.0 (2013.06.03)
diff --git a/model_utils/tests/fields.py b/model_utils/tests/fields.py
index b0cdcad..0c95815 100644
--- a/model_utils/tests/fields.py
+++ b/model_utils/tests/fields.py
@@ -1,30 +1,34 @@
-import json
-
 from django.db import models
-from django.core.serializers.json import DjangoJSONEncoder
+
+try:
+    unicode()
+    str_class = basestring
+except NameError:
+    str_class = str
+
+def with_metaclass(meta, base=object):
+    return meta("NewBase", (base,), {})
 
 
-class SimpleJSONField(models.TextField):
-
-    __metaclass__ = models.SubfieldBase
+class MutableField(with_metaclass(models.SubfieldBase, models.TextField)):
 
     def to_python(self, value):
-        if value == "":
+        if value == '':
             return None
 
         try:
-            if isinstance(value, basestring):
-                return json.loads(value)
+            if isinstance(value, str_class):
+                return [int(i) for i in value.split(',')]
         except ValueError:
             pass
 
         return value
 
     def get_db_prep_save(self, value, connection):
-        if value == "":
-            return None
+        if value is None:
+            return ''
 
-        if isinstance(value, dict):
-            value = json.dumps(value, cls=DjangoJSONEncoder)
+        if isinstance(value, list):
+            value = ','.join((str(i) for i in value))
 
-        return super(SimpleJSONField, self).get_db_prep_save(value, connection)
+        return super(MutableField, self).get_db_prep_save(value, connection)
diff --git a/model_utils/tests/models.py b/model_utils/tests/models.py
index af8ff95..a41cce7 100644
--- a/model_utils/tests/models.py
+++ b/model_utils/tests/models.py
@@ -5,7 +5,7 @@ from model_utils.models import TimeStampedModel, StatusModel, TimeFramedModel
 from model_utils.tracker import FieldTracker, ModelTracker
 from model_utils.managers import QueryManager, InheritanceManager, PassThroughManager
 from model_utils.fields import SplitField, MonitorField, StatusField
-from model_utils.tests.fields import SimpleJSONField
+from model_utils.tests.fields import MutableField
 from model_utils import Choices
 
 
@@ -235,6 +235,7 @@ class Spot(models.Model):
 class Tracked(models.Model):
     name = models.CharField(max_length=20)
     number = models.IntegerField()
+    mutable = MutableField()
 
     tracker = FieldTracker()
 
@@ -272,18 +273,10 @@ class TrackedMultiple(models.Model):
     number_tracker = FieldTracker(fields=['number'])
 
 
-class TrackedWithJsonField(models.Model):
-    name = models.CharField(max_length=20)
-    number = models.IntegerField()
-
-    props = SimpleJSONField()
-
-    tracker = FieldTracker()
-
-
 class ModelTracked(models.Model):
     name = models.CharField(max_length=20)
     number = models.IntegerField()
+    mutable = MutableField()
 
     tracker = ModelTracker()
 
diff --git a/model_utils/tests/tests.py b/model_utils/tests/tests.py
index daeaa5d..2c1c538 100644
--- a/model_utils/tests/tests.py
+++ b/model_utils/tests/tests.py
@@ -26,9 +26,9 @@ from model_utils.tests.models import (
     StatusPlainTuple, TimeFrame, Monitored, StatusManagerAdded,
     TimeFrameManagerAdded, Dude, SplitFieldAbstractParent, Car, Spot,
     ModelTracked, ModelTrackedFK, ModelTrackedNotDefault, ModelTrackedMultiple,
-    Tracked, TrackedFK, TrackedNotDefault, TrackedWithJsonField,
-    TrackedNonFieldAttr, TrackedMultiple, StatusFieldDefaultFilled,
-    StatusFieldDefaultNotFilled)
+    Tracked, TrackedFK, TrackedNotDefault,TrackedNonFieldAttr, TrackedMultiple,
+    StatusFieldDefaultFilled,StatusFieldDefaultNotFilled
+    )
 
 
 class GetExcerptTests(TestCase):
@@ -762,52 +762,61 @@ class FieldTrackerTests(FieldTrackerTestCase, FieldTrackerCommonTests):
         self.assertChanged(name=None, number=None)
         self.instance.name = ''
         self.assertChanged(name=None, number=None)
+        self.instance.mutable = [1,2,3]
+        self.assertChanged(name=None, number=None, mutable=None)
 
     def test_pre_save_has_changed(self):
-        self.assertHasChanged(name=True, number=False)
+        self.assertHasChanged(name=True, number=False, mutable=False)
         self.instance.name = 'new age'
-        self.assertHasChanged(name=True, number=False)
+        self.assertHasChanged(name=True, number=False, mutable=False)
         self.instance.number = 7
         self.assertHasChanged(name=True, number=True)
+        self.instance.mutable = [1,2,3]
+        self.assertHasChanged(name=True, number=True, mutable=True)
 
     def test_first_save(self):
-        self.assertHasChanged(name=True, number=False)
-        self.assertPrevious(name=None, number=None)
-        self.assertCurrent(name='', number=None, id=None)
+        self.assertHasChanged(name=True, number=False, mutable=False)
+        self.assertPrevious(name=None, number=None, mutable=None)
+        self.assertCurrent(name='', number=None, id=None, mutable=None)
         self.assertChanged(name=None)
         self.instance.name = 'retro'
         self.instance.number = 4
-        self.assertHasChanged(name=True, number=True)
-        self.assertPrevious(name=None, number=None)
-        self.assertCurrent(name='retro', number=4, id=None)
-        self.assertChanged(name=None, number=None)
+        self.instance.mutable = [1,2,3]
+        self.assertHasChanged(name=True, number=True, mutable=True)
+        self.assertPrevious(name=None, number=None, mutable=None)
+        self.assertCurrent(name='retro', number=4, id=None, mutable=[1,2,3])
+        self.assertChanged(name=None, number=None, mutable=None)
         # Django 1.4 doesn't have update_fields
         if django.VERSION >= (1, 5, 0):
             self.instance.save(update_fields=[])
-            self.assertHasChanged(name=True, number=True)
-            self.assertPrevious(name=None, number=None)
-            self.assertCurrent(name='retro', number=4, id=None)
-            self.assertChanged(name=None, number=None)
+            self.assertHasChanged(name=True, number=True, mutable=True)
+            self.assertPrevious(name=None, number=None, mutable=None)
+            self.assertCurrent(name='retro', number=4, id=None, mutable=[1,2,3])
+            self.assertChanged(name=None, number=None, mutable=None)
             with self.assertRaises(ValueError):
                 self.instance.save(update_fields=['number'])
 
     def test_post_save_has_changed(self):
-        self.update_instance(name='retro', number=4)
-        self.assertHasChanged(name=False, number=False)
+        self.update_instance(name='retro', number=4, mutable=[1,2,3])
+        self.assertHasChanged(name=False, number=False, mutable=False)
         self.instance.name = 'new age'
         self.assertHasChanged(name=True, number=False)
         self.instance.number = 8
         self.assertHasChanged(name=True, number=True)
+        self.instance.mutable[1] = 4
+        self.assertHasChanged(name=True, number=True, mutable=True)
         self.instance.name = 'retro'
-        self.assertHasChanged(name=False, number=True)
+        self.assertHasChanged(name=False, number=True, mutable=True)
 
     def test_post_save_previous(self):
-        self.update_instance(name='retro', number=4)
+        self.update_instance(name='retro', number=4, mutable=[1,2,3])
         self.instance.name = 'new age'
-        self.assertPrevious(name='retro', number=4)
+        self.assertPrevious(name='retro', number=4, mutable=[1,2,3])
+        self.instance.mutable[1] = 4
+        self.assertPrevious(name='retro', number=4, mutable=[1,2,3])
 
     def test_post_save_changed(self):
-        self.update_instance(name='retro', number=4)
+        self.update_instance(name='retro', number=4, mutable=[1,2,3])
         self.assertChanged()
         self.instance.name = 'new age'
         self.assertChanged(name='retro')
@@ -815,36 +824,48 @@ class FieldTrackerTests(FieldTrackerTestCase, FieldTrackerCommonTests):
         self.assertChanged(name='retro', number=4)
         self.instance.name = 'retro'
         self.assertChanged(number=4)
+        self.instance.mutable[1] = 4
+        self.assertChanged(number=4, mutable=[1,2,3])
+        self.instance.mutable = [1,2,3]
+        self.assertChanged(number=4)
 
     def test_current(self):
-        self.assertCurrent(id=None, name='', number=None)
+        self.assertCurrent(id=None, name='', number=None, mutable=None)
         self.instance.name = 'new age'
-        self.assertCurrent(id=None, name='new age', number=None)
+        self.assertCurrent(id=None, name='new age', number=None, mutable=None)
         self.instance.number = 8
-        self.assertCurrent(id=None, name='new age', number=8)
+        self.assertCurrent(id=None, name='new age', number=8, mutable=None)
+        self.instance.mutable = [1,2,3]
+        self.assertCurrent(id=None, name='new age', number=8, mutable=[1,2,3])
+        self.instance.mutable[1] = 4
+        self.assertCurrent(id=None, name='new age', number=8, mutable=[1,4,3])
         self.instance.save()
-        self.assertCurrent(id=self.instance.id, name='new age', number=8)
+        self.assertCurrent(id=self.instance.id, name='new age', number=8, mutable=[1,4,3])
 
     @skipUnless(
         django.VERSION >= (1, 5, 0), "Django 1.4 doesn't have update_fields")
     def test_update_fields(self):
-        self.update_instance(name='retro', number=4)
+        self.update_instance(name='retro', number=4, mutable=[1,2,3])
         self.assertChanged()
         self.instance.name = 'new age'
         self.instance.number = 8
-        self.assertChanged(name='retro', number=4)
+        self.instance.mutable = [4,5,6]
+        self.assertChanged(name='retro', number=4, mutable=[1,2,3])
         self.instance.save(update_fields=[])
-        self.assertChanged(name='retro', number=4)
+        self.assertChanged(name='retro', number=4, mutable=[1,2,3])
         self.instance.save(update_fields=['name'])
         in_db = self.tracked_class.objects.get(id=self.instance.id)
         self.assertEqual(in_db.name, self.instance.name)
         self.assertNotEqual(in_db.number, self.instance.number)
-        self.assertChanged(number=4)
+        self.assertChanged(number=4, mutable=[1,2,3])
         self.instance.save(update_fields=['number'])
+        self.assertChanged(mutable=[1,2,3])
+        self.instance.save(update_fields=['mutable'])
         self.assertChanged()
         in_db = self.tracked_class.objects.get(id=self.instance.id)
         self.assertEqual(in_db.name, self.instance.name)
         self.assertEqual(in_db.number, self.instance.number)
+        self.assertEqual(in_db.mutable, self.instance.mutable)
 
 
 class FieldTrackedModelCustomTests(FieldTrackerTestCase,
@@ -929,171 +950,6 @@ class FieldTrackedModelCustomTests(FieldTrackerTestCase,
         self.assertChanged()
 
 
-class JSONFieldTrackedModelTests(FieldTrackerTestCase):
-
-    tracked_class = TrackedWithJsonField
-
-    def setUp(self):
-        self.instance = self.tracked_class()
-        self.tracker = self.instance.tracker
-
-    def test_pre_save_changed(self):
-        self.assertChanged(name=None)
-        self.instance.name = 'new age'
-        self.assertChanged(name=None)
-        self.instance.number = 8
-        self.assertChanged(name=None, number=None)
-        self.instance.name = ''
-        self.assertChanged(name=None, number=None)
-        self.instance.props = {'attr': 1}
-        self.assertChanged(name=None, number=None, props=None)
-
-    def test_first_save(self):
-        self.assertHasChanged(name=True)
-        self.assertPrevious(name=None, number=None, props=None)
-        self.assertCurrent(name='', number=None, props=None, id=None)
-        self.assertChanged(name=None)
-        self.instance.name = 'retro'
-        self.instance.number = 4
-        self.instance.props = {'vodka': True}
-        self.assertHasChanged(name=True, number=True, props=True)
-        self.assertPrevious(name=None, number=None, props=None)
-        self.assertCurrent(name='retro', number=4,
-                           props={'vodka': True}, id=None)
-        self.assertChanged(name=None, number=None, props=None)
-
-    def test_pre_save_has_changed(self):
-        self.assertHasChanged(name=True)
-        self.instance.name = 'new age'
-        self.assertHasChanged(name=True)
-        self.instance.number = 7
-        self.assertHasChanged(name=True, number=True)
-        self.instance.props = {'bears_on_red_square': False}
-        self.assertChanged(name=None, number=None, props=None)
-
-    def test_post_save_has_changed(self):
-        self.update_instance(
-            name='retro', number=4,
-            props={
-                'goodies': {
-                    'balalaika': True,
-                    'Topol-M': True
-                }
-            }
-        )
-        self.assertHasChanged(name=False, number=False, props=False)
-        self.instance.name = 'new age'
-        self.assertHasChanged(name=True, number=False, props=False)
-        self.instance.number = 8
-        self.assertHasChanged(name=True, number=True)
-        self.instance.name = 'retro'
-        self.assertHasChanged(name=False, number=True)
-        self.instance.props = {
-            'goodies': {
-                'balalaika': False,
-                'Topol-M': True
-            }
-        }
-        self.assertHasChanged(name=False, number=True, props=True)
-
-    def test_post_save_previous(self):
-        self.update_instance(
-            name='retro', number=4,
-            props={
-                'goodies': {
-                    'balalaika': True,
-                    'Topol-M': True
-                }
-            }
-        )
-        self.instance.name = 'new age'
-        self.instance.props = {
-            'goodies': {
-                'balalaika': False,
-                'Topol-M': True
-            }
-        }
-        self.assertPrevious(
-            name='retro',
-            number=4,
-            props={
-                'goodies': {
-                    'balalaika': True,
-                    'Topol-M': True
-                }
-            }
-        )
-
-    def test_post_save_changed(self):
-        self.update_instance(
-            name='retro', number=4,
-            props={
-                'goodies': {
-                    'balalaika': True,
-                    'Topol-M': True
-                }
-            }
-        )
-        self.assertChanged()
-        self.instance.name = 'new age'
-        self.assertChanged(name='retro')
-        self.instance.number = 8
-        self.assertChanged(name='retro', number=4)
-        self.instance.name = 'retro'
-        self.assertChanged(number=4)
-        self.instance.props = {
-            'goodies': {
-                'balalaika': False,
-                'Topol-M': True
-            }
-        }
-        self.assertChanged(
-            number=4,
-            props={
-                'goodies': {
-                    'balalaika': True,
-                    'Topol-M': True
-                }
-            }
-        )
-
-    def test_current(self):
-        self.assertCurrent(name='', number=None, props=None, id=None)
-        self.instance.name = 'new age'
-        self.assertCurrent(name='new age', number=None, props=None, id=None)
-        self.instance.number = 8
-        self.assertCurrent(name='new age', number=8, props=None, id=None)
-        self.instance.props = {
-            'goodies': {
-                'balalaika': False,
-                'Topol-M': True
-            }
-        }
-        self.assertCurrent(
-            name='new age',
-            number=8,
-            props={
-                'goodies': {
-                    'balalaika': False,
-                    'Topol-M': True
-                }
-            },
-            id=None
-        )
-        self.instance.save()
-        self.assertCurrent(
-            name='new age',
-            number=8,
-            props={
-                'goodies': {
-                    'balalaika': False,
-                    'Topol-M': True
-                }
-            },
-            id=self.instance.id
-        )
-
-
 class FieldTrackedModelAttributeTests(FieldTrackerTestCase):
 
     tracked_class = TrackedNonFieldAttr
@@ -1291,24 +1147,27 @@ class ModelTrackerTests(FieldTrackerTests):
         self.assertChanged()
         self.instance.name = ''
         self.assertChanged()
+        self.instance.mutable = [1,2,3]
+        self.assertChanged()
 
     def test_first_save(self):
-        self.assertHasChanged(name=True, number=True)
-        self.assertPrevious(name=None, number=None)
-        self.assertCurrent(name='', number=None, id=None)
+        self.assertHasChanged(name=True, number=True, mutable=True)
+        self.assertPrevious(name=None, number=None, mutable=None)
+        self.assertCurrent(name='', number=None, id=None, mutable=None)
         self.assertChanged()
         self.instance.name = 'retro'
         self.instance.number = 4
-        self.assertHasChanged(name=True, number=True)
-        self.assertPrevious(name=None, number=None)
-        self.assertCurrent(name='retro', number=4, id=None)
+        self.instance.mutable = [1,2,3]
+        self.assertHasChanged(name=True, number=True, mutable=True)
+        self.assertPrevious(name=None, number=None, mutable=None)
+        self.assertCurrent(name='retro', number=4, id=None, mutable=[1,2,3])
         self.assertChanged()
         # Django 1.4 doesn't have update_fields
         if django.VERSION >= (1, 5, 0):
             self.instance.save(update_fields=[])
-            self.assertHasChanged(name=True, number=True)
-            self.assertPrevious(name=None, number=None)
-            self.assertCurrent(name='retro', number=4, id=None)
+            self.assertHasChanged(name=True, number=True, mutable=True)
+            self.assertPrevious(name=None, number=None, mutable=None)
+            self.assertCurrent(name='retro', number=4, id=None, mutable=[1,2,3])
             self.assertChanged()
             with self.assertRaises(ValueError):
                 self.instance.save(update_fields=['number'])
diff --git a/model_utils/tracker.py b/model_utils/tracker.py
index a08a958..fa43c57 100644
--- a/model_utils/tracker.py
+++ b/model_utils/tracker.py
@@ -1,7 +1,6 @@
 from __future__ import unicode_literals
 
 from copy import deepcopy
-from json import JSONEncoder
 
 from django.db import models
 from django.core.exceptions import FieldError
@@ -23,7 +22,10 @@ class FieldInstanceTracker(object):
             self.saved_data = self.current()
         else:
             self.saved_data.update(**self.current(fields=fields))
-        return self.saved_data
+
+        # preventing mutable fields side effects
+        for field, field_value in self.saved_data.items():
+            self.saved_data[field] = deepcopy(field_value)
 
     def current(self, fields=None):
         """Return dict of current values for all tracked fields"""
@@ -82,8 +84,7 @@ class FieldTracker(object):
     def initialize_tracker(self, sender, instance, **kwargs):
         tracker = self.tracker_class(instance, self.fields, self.field_map)
         setattr(instance, self.attname, tracker)
-        saved_data = tracker.set_saved_fields()
-        self.prevent_json_fields_side_effects(saved_data)
+        tracker.set_saved_fields()
         self.patch_save(instance)
 
     def patch_save(self, instance):
@@ -106,16 +107,6 @@ class FieldTracker(object):
             return ret
         instance.save = save
 
-    def prevent_json_fields_side_effects(self, saved_data):
-        for field, field_value in saved_data.items():
-            if isinstance(field_value, (dict, list, tuple)):
-                try:
-                    JSONEncoder().encode(field_value)
-                except TypeError:
-                    pass
-                else:
-                    saved_data[field] = deepcopy(field_value)
-
     def __get__(self, instance, owner):
         if instance is None:
             return self