diff --git a/IPython/utils/tests/test_traitlets.py b/IPython/utils/tests/test_traitlets.py
index ef9024b..6f1592a 100644
--- a/IPython/utils/tests/test_traitlets.py
+++ b/IPython/utils/tests/test_traitlets.py
@@ -25,10 +25,11 @@ import re
 import sys
 from unittest import TestCase
 
+import nose.tools as nt
 from nose import SkipTest
 
 from IPython.utils.traitlets import (
-    HasTraits, MetaHasTraits, TraitType, Any, CBytes,
+    HasTraits, MetaHasTraits, TraitType, Any, CBytes, Dict,
     Int, Long, Integer, Float, Complex, Bytes, Unicode, TraitError,
     Undefined, Type, This, Instance, TCPAddress, List, Tuple,
     ObjectName, DottedObjectName, CRegExp
@@ -906,3 +907,14 @@ class TestCRegExp(TraitTestBase):
     _default_value = re.compile(r'')
     _good_values = [r'\d+', re.compile(r'\d+')]
     _bad_values = [r'(', None, ()]
+
+class DictTrait(HasTraits):
+    value = Dict()
+
+def test_dict_assignment():
+    d = dict()
+    c = DictTrait()
+    c.value = d
+    d['a'] = 5
+    nt.assert_equal(d, c.value)
+    nt.assert_true(c.value is d)
diff --git a/IPython/utils/traitlets.py b/IPython/utils/traitlets.py
index 8a40133..cd08d4b 100644
--- a/IPython/utils/traitlets.py
+++ b/IPython/utils/traitlets.py
@@ -309,8 +309,8 @@ class TraitType(object):
     def __set__(self, obj, value):
         new_value = self._validate(obj, value)
         old_value = self.__get__(obj)
+        obj._trait_values[self.name] = new_value
         if old_value != new_value:
-            obj._trait_values[self.name] = new_value
             obj._notify_trait(self.name, old_value, new_value)
 
     def _validate(self, obj, value):