diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 0d7c4edd00..dc455dcc8c 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -568,6 +568,13 @@ class DateField(Field):
         else:
             return self.editable or self.auto_now or self.auto_now_add
 
+    def get_db_prep_lookup(self, lookup_type, value):
+        # For "__month" and "__day" lookups, convert the value to a string so
+        # the database backend always sees a consistent type.
+        if lookup_type in ('month', 'day'):
+            return [force_unicode(value)]
+        return super(DateField, self).get_db_prep_lookup(lookup_type, value)
+
     def get_db_prep_value(self, value):
         # Casts dates into the format expected by the backend
         return connection.ops.value_to_db_date(self.to_python(value))
diff --git a/tests/regressiontests/model_regress/models.py b/tests/regressiontests/model_regress/models.py
index 9e11b43d2b..d79bbca3be 100644
--- a/tests/regressiontests/model_regress/models.py
+++ b/tests/regressiontests/model_regress/models.py
@@ -57,18 +57,26 @@ u''
 >>> len(a4.article_text)
 5000
 
-# #659 regression test
+# Regression test for #659
 >>> import datetime
 >>> p = Party.objects.create(when = datetime.datetime(1999, 12, 31))
 >>> p = Party.objects.create(when = datetime.datetime(1998, 12, 31))
 >>> p = Party.objects.create(when = datetime.datetime(1999, 1, 1))
->>> [p.when for p in Party.objects.filter(when__month = 2)]
+>>> [p.when for p in Party.objects.filter(when__month=2)]
 []
->>> [p.when for p in Party.objects.filter(when__month = 1)]
+>>> [p.when for p in Party.objects.filter(when__month=1)]
 [datetime.date(1999, 1, 1)]
->>> [p.when for p in Party.objects.filter(when__month = 12)]
+>>> [p.when for p in Party.objects.filter(when__month=12)]
 [datetime.date(1999, 12, 31), datetime.date(1998, 12, 31)]
->>> [p.when for p in Party.objects.filter(when__year = 1998)]
+>>> [p.when for p in Party.objects.filter(when__year=1998)]
+[datetime.date(1998, 12, 31)]
+
+# Regression test for #8510
+>>> [p.when for p in Party.objects.filter(when__day='31')]
+[datetime.date(1999, 12, 31), datetime.date(1998, 12, 31)]
+>>> [p.when for p in Party.objects.filter(when__month='12')]
+[datetime.date(1999, 12, 31), datetime.date(1998, 12, 31)]
+>>> [p.when for p in Party.objects.filter(when__year='1998')]
 [datetime.date(1998, 12, 31)]
 
 # Check that get_next_by_FIELD and get_previous_by_FIELD don't crash when we