diff --git a/sklearn2pmml/cross_reference/__init__.py b/sklearn2pmml/cross_reference/__init__.py
index 2b13428..7b61049 100644
--- a/sklearn2pmml/cross_reference/__init__.py
+++ b/sklearn2pmml/cross_reference/__init__.py
@@ -16,12 +16,17 @@ def __getitem__(self, key):
 	def __setitem__(self, key, value):
 		self.data[key] = value
 
-	def clear(self):
-		self.data.clear()
-
 	def __len__(self):
 		return len(self.data)
 
+	def __copy__(self):
+		return self
+
+	def __deepcopy__(self, memo):
+		result = self
+		memo[id(self)] = result
+		return result
+
 	def __getstate__(self):
 		state = self.__dict__.copy()
 		state["data"] = dict()
@@ -30,6 +35,9 @@ def __getstate__(self):
 	def __setstate__(self, state):
 		self.__dict__.update(state)
 
+	def clear(self):
+		self.data.clear()
+
 def make_memorizer_union(memory, names, transform_only = True):
 	return FeatureUnion([
 		("memorizer", Memorizer(memory, names, transform_only = transform_only)),
diff --git a/sklearn2pmml/cross_reference/tests/__init__.py b/sklearn2pmml/cross_reference/tests/__init__.py
index 0dfcb5f..a2178ea 100644
--- a/sklearn2pmml/cross_reference/tests/__init__.py
+++ b/sklearn2pmml/cross_reference/tests/__init__.py
@@ -1,8 +1,10 @@
 from pandas import DataFrame
+from sklearn.base import clone
 from sklearn.pipeline import make_pipeline
 from sklearn2pmml.cross_reference import make_memorizer_union, make_recaller_union, Memory, Memorizer, Recaller
 from unittest import TestCase
 
+import copy
 import numpy
 import pickle
 
@@ -19,6 +21,13 @@ def test_item_assignment(self):
 		memory.clear()
 		self.assertEqual(0, len(memory))
 
+	def test_copy(self):
+		memory = Memory()
+		memory_copy = copy.copy(memory)
+		self.assertIs(memory, memory_copy)
+		memory_deepcopy = copy.deepcopy(memory)
+		self.assertIs(memory, memory_deepcopy)
+
 	def test_pickle(self):
 		memory = Memory()
 		memory["int"] = [1, 2, 3]
@@ -60,6 +69,13 @@ def test_transform(self):
 		self.assertEqual([1.0, 2.0, 3.0], memory["float"].astype(float).tolist())
 		self.assertEqual(["one", "two", "three"], memory["str"].tolist())
 
+	def test_clone(self):
+		memory = Memory()
+		memorizer = Memorizer(memory, ["flag"])
+		memorizer_clone = clone(memorizer)
+		self.assertIsNot(memorizer, memorizer_clone)
+		self.assertIs(memorizer.memory, memorizer_clone.memory)
+
 class RecallerTest(TestCase):
 
 	def test_transform(self):
@@ -90,6 +106,13 @@ def test_transform(self):
 		self.assertEqual([1.0, 2.0, 3.0], Xt[:, 1].tolist())
 		self.assertEqual(["one", "two", "three"], Xt[:, 2].tolist())
 
+	def test_clone(self):
+		memory = Memory()
+		recaller = Recaller(memory, ["flag"])
+		recaller_clone = clone(recaller)
+		self.assertIsNot(recaller, recaller_clone)
+		self.assertIs(recaller.memory, recaller_clone.memory)
+
 class FunctionTest(TestCase):
 
 	def test_make_memorizer_union(self):