diff --git a/wsme/tests/test_types.py b/wsme/tests/test_types.py
index 1c28495..a0a3cd1 100644
--- a/wsme/tests/test_types.py
+++ b/wsme/tests/test_types.py
@@ -523,3 +523,107 @@ Value: 'v3'. Value should be one of: v., v.",
                 return 'from-file'
         f = types.File(content=six.b('from-content'))
         assert f.file.read() == six.b('from-content')
+
+    def test_unregister(self):
+        class TempType(object):
+            pass
+        types.registry.register(TempType)
+        v = types.registry.lookup('TempType')
+        self.assertIs(v, TempType)
+        types.registry._unregister(TempType)
+        after = types.registry.lookup('TempType')
+        self.assertIs(after, None)
+
+    def test_unregister_twice(self):
+        class TempType(object):
+            pass
+        types.registry.register(TempType)
+        v = types.registry.lookup('TempType')
+        self.assertIs(v, TempType)
+        types.registry._unregister(TempType)
+        # Second call should not raise an exception
+        types.registry._unregister(TempType)
+        after = types.registry.lookup('TempType')
+        self.assertIs(after, None)
+
+    def test_unregister_array_type(self):
+        class TempType(object):
+            pass
+        t = [TempType]
+        types.registry.register(t)
+        self.assertNotEqual(types.registry.array_types, set())
+        types.registry._unregister(t)
+        self.assertEqual(types.registry.array_types, set())
+
+    def test_unregister_array_type_twice(self):
+        class TempType(object):
+            pass
+        t = [TempType]
+        types.registry.register(t)
+        self.assertNotEqual(types.registry.array_types, set())
+        types.registry._unregister(t)
+        # Second call should not raise an exception
+        types.registry._unregister(t)
+        self.assertEqual(types.registry.array_types, set())
+
+    def test_unregister_dict_type(self):
+        class TempType(object):
+            pass
+        t = {str: TempType}
+        types.registry.register(t)
+        self.assertNotEqual(types.registry.dict_types, set())
+        types.registry._unregister(t)
+        self.assertEqual(types.registry.dict_types, set())
+
+    def test_unregister_dict_type_twice(self):
+        class TempType(object):
+            pass
+        t = {str: TempType}
+        types.registry.register(t)
+        self.assertNotEqual(types.registry.dict_types, set())
+        types.registry._unregister(t)
+        # Second call should not raise an exception
+        types.registry._unregister(t)
+        self.assertEqual(types.registry.dict_types, set())
+
+    def test_reregister(self):
+        class TempType(object):
+            pass
+        types.registry.register(TempType)
+        v = types.registry.lookup('TempType')
+        self.assertIs(v, TempType)
+        types.registry.reregister(TempType)
+        after = types.registry.lookup('TempType')
+        self.assertIs(after, TempType)
+
+    def test_reregister_and_add_attr(self):
+        class TempType(object):
+            pass
+        types.registry.register(TempType)
+        attrs = types.list_attributes(TempType)
+        self.assertEqual(attrs, [])
+        TempType.one = str
+        types.registry.reregister(TempType)
+        after = types.list_attributes(TempType)
+        self.assertNotEqual(after, [])
+
+    def test_dynamicbase_add_attributes(self):
+        class TempType(types.DynamicBase):
+            pass
+        types.registry.register(TempType)
+        attrs = types.list_attributes(TempType)
+        self.assertEqual(attrs, [])
+        TempType.add_attributes(one=str)
+        after = types.list_attributes(TempType)
+        self.assertEqual(len(after), 1)
+
+    def test_dynamicbase_add_attributes_second(self):
+        class TempType(types.DynamicBase):
+            pass
+        types.registry.register(TempType)
+        attrs = types.list_attributes(TempType)
+        self.assertEqual(attrs, [])
+        TempType.add_attributes(one=str)
+        TempType.add_attributes(two=int)
+        after = types.list_attributes(TempType)
+        self.assertEqual(len(after), 2)
diff --git a/wsme/types.py b/wsme/types.py
index 0902ce3..1193ee9 100644
--- a/wsme/types.py
+++ b/wsme/types.py
@@ -670,6 +670,41 @@ class Registry(object):
         self._complex_types.append(weakref.ref(class_))
         return class_
 
+    def reregister(self, class_):
+        """Register a type which may already have been registered.
+        """
+        self._unregister(class_)
+        return self.register(class_)
+
+    def _unregister(self, class_):
+        """Remove a previously registered type.
+        """
+        # Clear the existing attribute reference so it is rebuilt if
+        # the class is registered again later.
+        if hasattr(class_, '_wsme_attributes'):
+            del class_._wsme_attributes
+        # FIXME(dhellmann): This method does not recurse through the
+        # types like register() does. Should it?
+        if isinstance(class_, list):
+            at = ArrayType(class_[0])
+            try:
+                self.array_types.remove(at)
+            except KeyError:
+                pass
+        elif isinstance(class_, dict):
+            key_type, value_type = list(class_.items())[0]
+            self.dict_types = set(
+                dt for dt in self.dict_types
+                if (dt.key_type, dt.value_type) != (key_type, value_type)
+            )
+        # We can't use remove() here because the items in
+        # _complex_types are weakref objects pointing to the classes,
+        # so we can't compare with them directly.
+        self._complex_types = [
+            ct for ct in self._complex_types
+            if ct() is not class_
+        ]
+
     def lookup(self, typename):
         log.debug('Lookup %s' % typename)
         modname = None
@@ -772,3 +807,26 @@ class File(Base):
         if self._file is None and self._content:
             self._file = six.BytesIO(self._content)
         return self._file
+
+
+class DynamicBase(Base):
+    """Base type for complex types for which all attributes are not
+    defined when the class is constructed.
+
+    This class is meant to be used as a base for types that have
+    properties added after the main class is created, such as by
+    loading plugins.
+
+    """
+
+    @classmethod
+    def add_attributes(cls, **attrs):
+        """Add more attributes
+
+        The arguments should be valid Python attribute names
+        associated with a type for the new attribute.
+
+        """
+        for n, t in attrs.items():
+            setattr(cls, n, t)
+        cls.__registry__.reregister(cls)