diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index 8b036bacd2..57bdea17f4 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -452,9 +452,13 @@ class NullBooleanSelect(Select):
                 False: False}.get(value, None)
 
     def _has_changed(self, initial, data):
-        # Sometimes data or initial could be None or u'' which should be the
-        # same thing as False.
-        return bool(initial) != bool(data)
+        # For a NullBooleanSelect, None (unknown) and False (No)
+        # are not the same
+        if initial is not None:
+            initial = bool(initial)
+        if data is not None:
+            data = bool(data)
+        return initial != data
 
 class SelectMultiple(Select):
     def render(self, name, value, attrs=None, choices=()):
diff --git a/tests/regressiontests/forms/widgets.py b/tests/regressiontests/forms/widgets.py
index d909c0f26c..4acaf831aa 100644
--- a/tests/regressiontests/forms/widgets.py
+++ b/tests/regressiontests/forms/widgets.py
@@ -532,6 +532,20 @@ Choices can be nested one level in order to create HTML optgroups:
 <option value="2">Yes</option>
 <option value="3" selected="selected">No</option>
 </select>
+>>> w._has_changed(False, None)
+True
+>>> w._has_changed(None, False)
+True
+>>> w._has_changed(None, None)
+False
+>>> w._has_changed(False, False)
+False
+>>> w._has_changed(True, False)
+True
+>>> w._has_changed(True, None)
+True
+>>> w._has_changed(True, True)
+False
 
 """ + \
 r""" # [This concatenation is to keep the string below the jython's 32K limit].