diff --git a/changelog.rst b/changelog.rst
index 18de71d..04ae81a 100644
--- a/changelog.rst
+++ b/changelog.rst
@@ -7,6 +7,7 @@ changelog
 - Implement the instance ACLs interface.
 - Implement the instance bound ACLs interface.
 - Implement the auth._verify method for token verification.
+- Allowing instances to be extensible.
 
 0.3.x
 -----
diff --git a/objectrocket/__init__.py b/objectrocket/__init__.py
index 904ab52..455b993 100644
--- a/objectrocket/__init__.py
+++ b/objectrocket/__init__.py
@@ -2,5 +2,5 @@
 # Import this object for ease of access.
 from objectrocket.client import Client  # noqa
 
-VERSION = ('0', '4', '0')
+VERSION = ('0', '4', '1')
 __version__ = '.'.join(VERSION)
diff --git a/objectrocket/bases.py b/objectrocket/bases.py
index a928369..971d50b 100644
--- a/objectrocket/bases.py
+++ b/objectrocket/bases.py
@@ -293,6 +293,7 @@ def _register_extensions(self, namespace):
             'extensions.classes.{}'.format(namespace),
             propagate_map_exceptions=True
         )
+
         if extmanager.extensions:
             extmanager.map(util.register_extension_class, base=self)
 
diff --git a/objectrocket/instances/__init__.py b/objectrocket/instances/__init__.py
index 2037598..5ebcc1d 100644
--- a/objectrocket/instances/__init__.py
+++ b/objectrocket/instances/__init__.py
@@ -14,7 +14,7 @@
 logger = logging.getLogger(__name__)
 
 
-class Instances(bases.BaseOperationsLayer):
+class Instances(bases.BaseOperationsLayer, bases.Extensible):
     """Instance operations.
 
     :param objectrocket.client.Client base_client: An instance of objectrocket.client.Client.
@@ -23,6 +23,9 @@ class Instances(bases.BaseOperationsLayer):
     def __init__(self, base_client):
         super(Instances, self).__init__(base_client=base_client)
 
+        # Register any extensions for this class.
+        self._register_extensions('objectrocket.instances.Instances')
+
     #####################
     # Public interface. #
     #####################