diff --git a/docs/release_notes.rst b/docs/release_notes.rst
index 0272a572..7fadbcd8 100644
--- a/docs/release_notes.rst
+++ b/docs/release_notes.rst
@@ -16,7 +16,7 @@ Breaking changes:
     If your codebase uses :py:class:`~pynamodb.attributes.BinaryAttribute` or :py:class:`~pynamodb.attributes.BinarySetAttribute`,
     go over the attribute declarations and mark them accordingly.
   * When using binary attributes, the return value of :meth:`~pynamodb.models.Model.serialize` will no longer be JSON-serializable
-    since it will contain :code:`bytes` objects. Use :meth:`~pynamodb.models.Model.to_dynamodb_dict`
+    since it will contain :code:`bytes` objects. Use :meth:`~pynamodb.attributes.AttributeContainer.to_dynamodb_dict` and :meth:`~pynamodb.attributes.AttributeContainer.to_simple_dict` for JSON-serializable mappings.
     for a safe JSON-serializable representation.
 
 * Python 3.6 is no longer supported.
diff --git a/pynamodb/attributes.py b/pynamodb/attributes.py
index ce750bf4..964b5ae6 100644
--- a/pynamodb/attributes.py
+++ b/pynamodb/attributes.py
@@ -929,7 +929,7 @@ class MapAttribute(Attribute[Mapping[_KT, _VT]], AttributeContainer, metaclass=M
     For example, below we define "MyModel" which contains a MapAttribute "my_map":
 
     class MyModel(Model):
-       my_map = MapAttribute(attr_name="dynamo_name", default={})
+       my_map = MapAttribute(attr_name="dynamo_name", default=dict)
 
     When instantiated in this manner (as a class attribute of an AttributeContainer class), the MapAttribute
     class acts as an instance of the Attribute class. The instance stores data about the attribute (in this