diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 30768be7..f97b7560 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -1,6 +1,10 @@
 Changelog
 =========
 
+UNRELEASED
+----------
+ * Added ``has_changed()`` method to ``taggit.forms.TagField``.
+
 0.24.0 (2019-02-19)
 ~~~~~~~~~~~~~~~~~~~
  * The project has moved to `Jazzband <https://jazzband.co/>`_. This is the
diff --git a/taggit/forms.py b/taggit/forms.py
index e7c493f8..a4ec88dd 100644
--- a/taggit/forms.py
+++ b/taggit/forms.py
@@ -10,7 +10,7 @@
 class TagWidget(forms.TextInput):
     def format_value(self, value):
         if value is not None and not isinstance(value, six.string_types):
-            value = edit_string_for_tags([o.tag for o in value.select_related("tag")])
+            value = edit_string_for_tags(value)
 
         return super(TagWidget, self).format_value(value)
 
@@ -26,3 +26,12 @@ def clean(self, value):
             raise forms.ValidationError(
                 _("Please provide a comma-separated list of tags.")
             )
+
+    def has_changed(self, initial_value, data_value):
+        initial_value = [tag.name for tag in initial_value]
+        initial_value.sort()
+        try:
+            data_value = self.clean(data_value)
+        except forms.ValidationError:
+            pass
+        return initial_value != data_value
diff --git a/taggit/managers.py b/taggit/managers.py
index 508cb8bb..814a3c8f 100644
--- a/taggit/managers.py
+++ b/taggit/managers.py
@@ -531,10 +531,13 @@ def formfield(self, form_class=TagField, **kwargs):
         defaults.update(kwargs)
         return form_class(**defaults)
 
-    def value_from_object(self, instance):
-        if instance.pk:
-            return self.through.objects.filter(**self.through.lookup_kwargs(instance))
-        return self.through.objects.none()
+    def value_from_object(self, obj):
+        if obj.pk is None:
+            return []
+        qs = self.through.objects.select_related("tag").filter(
+            **self.through.lookup_kwargs(obj)
+        )
+        return [ti.tag for ti in qs]
 
     def related_query_name(self):
         return self.model._meta.model_name
diff --git a/tests/tests.py b/tests/tests.py
index 00daa8fc..df6ce802 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -885,6 +885,67 @@ def test_formfield(self):
         ff = tm.formfield()
         self.assertRaises(ValidationError, ff.clean, "")
 
+    def test_form_changed_data(self):
+        # new food, blank tag
+        pear = self.food_model()
+        request = {"name": "pear", "tags": ""}
+        fff = self.form_class(request, instance=pear)
+        self.assertFalse(fff.is_valid())
+
+        pear = self.food_model()
+        request = {"name": "pear", "tags": "sweat"}
+        fff = self.form_class(request, instance=pear)
+        self.assertTrue(fff.is_valid())
+        self.assertIn("tags", fff.changed_data)
+        self.assertIn("name", fff.changed_data)
+        fff.save()
+
+        request = {"name": "pear", "tags": "yellow"}
+        fff = self.form_class(request, instance=pear)
+        self.assertTrue(fff.is_valid())
+        self.assertIn("tags", fff.changed_data)
+        self.assertNotIn("name", fff.changed_data)
+        fff.save()
+
+        # same object nothing changed
+        fff = self.form_class(request, instance=pear)
+        self.assertTrue(fff.is_valid())
+        self.assertFalse(fff.changed_data)
+
+        # delete tag
+        request = {"name": "pear", "tags": ""}
+        fff = self.form_class(request, instance=pear)
+        self.assertFalse(fff.is_valid())  # tag not blank
+
+        # change name, tags are the same
+        request = {"name": "apple", "tags": "yellow"}
+        fff = self.form_class(request, instance=pear)
+        self.assertTrue(fff.is_valid())
+        self.assertIn("name", fff.changed_data)
+        self.assertNotIn("tags", fff.changed_data)
+        fff.save()
+
+        # tags changed
+        apple = self.food_model.objects.get(name="apple")
+        request = {"name": "apple", "tags": "yellow, delicious"}
+        fff = self.form_class(request, instance=apple)
+        self.assertTrue(fff.is_valid())
+        self.assertNotIn("name", fff.changed_data)
+        self.assertIn("tags", fff.changed_data)
+        fff.save()
+
+        # only tags order changed
+        apple = self.food_model.objects.get(name="apple")
+        request = {"name": "apple", "tags": "delicious, yellow"}
+        fff = self.form_class(request, instance=apple)
+        self.assertTrue(fff.is_valid())
+        self.assertFalse(fff.changed_data)
+
+        # and nothing changed
+        fff = self.form_class(request, instance=apple)
+        self.assertTrue(fff.is_valid())
+        self.assertFalse(fff.changed_data)
+
 
 class TaggableFormDirectTestCase(TaggableFormTestCase):
     form_class = DirectFoodForm