diff --git a/mopidy/models.py b/mopidy/models.py
index 39d29fd3..b1f0b351 100644
--- a/mopidy/models.py
+++ b/mopidy/models.py
@@ -87,7 +87,9 @@ class ImmutableObject(object):
             public_key = key.lstrip('_')
             value = self.__dict__[key]
             if isinstance(value, (set, frozenset, list, tuple)):
-                value = [o.serialize() for o in value]
+                value = [
+                    v.serialize() if isinstance(v, ImmutableObject) else v
+                    for v in value]
             elif isinstance(value, ImmutableObject):
                 value = value.serialize()
             if value:
diff --git a/tests/models_test.py b/tests/models_test.py
index 08a8c6f0..c2d65ec6 100644
--- a/tests/models_test.py
+++ b/tests/models_test.py
@@ -255,6 +255,13 @@ class AlbumTest(unittest.TestCase):
                 'artists': [artist.serialize()]},
             Album(uri='uri', name='name', artists=[artist]).serialize())
 
+    def test_serialize_with_images(self):
+        image = 'data:foobar'
+        self.assertDictEqual(
+            {'__model__': 'Album', 'uri': 'uri', 'name': 'name',
+                'images': [image]},
+            Album(uri='uri', name='name', images=[image]).serialize())
+
     def test_to_json_and_back(self):
         album1 = Album(uri='uri', name='name', artists=[Artist(name='foo')])
         serialized = json.dumps(album1, cls=ModelJSONEncoder)