diff --git a/django/forms/extras/widgets.py b/django/forms/extras/widgets.py
index 4fb4869e689..65d6bf15f5d 100644
--- a/django/forms/extras/widgets.py
+++ b/django/forms/extras/widgets.py
@@ -136,6 +136,9 @@ class SelectDateWidget(Widget):
         return select_html
 
     def _has_changed(self, initial, data):
-        input_format = get_format('DATE_INPUT_FORMATS')[0]
-        data = datetime_safe.datetime.strptime(data, input_format).date()
-        return super(SelectDateWidget, self)._has_changed(initial, data)
\ No newline at end of file
+        try:
+            input_format = get_format('DATE_INPUT_FORMATS')[0]
+            data = datetime_safe.datetime.strptime(data, input_format).date()
+        except (TypeError, ValueError):
+            pass
+        return super(SelectDateWidget, self)._has_changed(initial, data)
diff --git a/tests/regressiontests/forms/tests/extra.py b/tests/regressiontests/forms/tests/extra.py
index 3c5dfabb615..c873af7a8ca 100644
--- a/tests/regressiontests/forms/tests/extra.py
+++ b/tests/regressiontests/forms/tests/extra.py
@@ -18,6 +18,9 @@ from .error_messages import AssertFormErrorsMixin
 class GetDate(Form):
     mydate = DateField(widget=SelectDateWidget)
 
+class GetNotRequiredDate(Form):
+    mydate = DateField(widget=SelectDateWidget, required=False)
+
 class GetDateShowHiddenInitial(Form):
     mydate = DateField(widget=SelectDateWidget, show_hidden_initial=True)
 
@@ -619,6 +622,15 @@ class FormsExtraTestCase(TestCase, AssertFormErrorsMixin):
         self.assertTrue(FormWithFile().is_multipart())
         self.assertTrue(FormWithImage().is_multipart())
 
+    def test_field_not_required(self):
+        b = GetNotRequiredDate({
+            'mydate_year': '',
+            'mydate_month': '',
+            'mydate_day': ''
+        })
+        self.assertFalse(b.has_changed())
+
+
 
 class FormsExtraL10NTestCase(TestCase):
     def setUp(self):