diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index b12c507f..b2aab5a4 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -537,7 +537,11 @@ class MapField(BaseField):
         return dict( [(key,self.field.to_mongo(item)) for key,item in value.iteritems()] )
 
     def prepare_query_value(self, op, value):
-        return self.field.prepare_query_value(op, value)
+        if op not in ('set', 'unset'):
+            return self.field.prepare_query_value(op, value)
+        for key in value:
+            value[key] = self.field.prepare_query_value(op, value[key])
+        return value
 
     def lookup_member(self, member_name):
         return self.field.lookup_member(member_name)
diff --git a/tests/queryset.py b/tests/queryset.py
index a2d78d72..82cd870d 100644
--- a/tests/queryset.py
+++ b/tests/queryset.py
@@ -261,6 +261,44 @@ class QuerySetTest(unittest.TestCase):
 
         Blog.drop_collection()
 
+    def test_mapfield_update(self):
+        """Ensure that the MapField can be updated."""
+        class Member(EmbeddedDocument):
+            gender = StringField()
+            age = IntField()
+
+        class Club(Document):
+            members = MapField(EmbeddedDocumentField(Member))
+
+        Club.drop_collection()
+
+        club = Club()
+        club.members['John'] = Member(gender="M", age=13)
+        club.save()
+
+        Club.objects().update(
+            set__members={"John": Member(gender="F", age=14)})
+
+        club = Club.objects().first()
+        self.assertEqual(club.members['John'].gender, "F")
+        self.assertEqual(club.members['John'].age, 14)
+
+    def test_dictfield_update(self):
+        """Ensure that the MapField can be updated."""
+        class Club(Document):
+            members = DictField()
+
+        club = Club()
+        club.members['John'] = dict(gender="M", age=13)
+        club.save()
+
+        Club.objects().update(
+            set__members={"John": dict(gender="F", age=14)})
+
+        club = Club.objects().first()
+        self.assertEqual(club.members['John']['gender'], "F")
+        self.assertEqual(club.members['John']['age'], 14)
+
     def test_get_or_create(self):
         """Ensure that ``get_or_create`` returns one result or creates a new
         document.