diff --git a/CHANGES.md b/CHANGES.md
index 0ca5a92b4..577567111 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -4,9 +4,6 @@
 - Fix a bug affecting dynamic modules occuring with modified builtins
   ([issue #316](https://github.com/cloudpipe/cloudpickle/issues/316))
 
-1.2.3
-=====
-
 - Fix a bug affecting cloudpickle when non-modules objects are added into
   sys.modules
   ([PR #326](https://github.com/cloudpipe/cloudpickle/pull/326)).
@@ -23,6 +20,10 @@
   https://docs.python.org/3/library/pickle.html#example
   ([issue #308](https://github.com/cloudpipe/cloudpickle/pull/308))
 
+- Fix a side effect that would redefine `types.ClassTypes` as `type`
+  when importing cloudpickle.
+  ([issue #337](https://github.com/cloudpipe/cloudpickle/pull/337))
+
 1.2.2
 =====
 
diff --git a/cloudpickle/__init__.py b/cloudpickle/__init__.py
index 0369eec03..f0c49bbb2 100644
--- a/cloudpickle/__init__.py
+++ b/cloudpickle/__init__.py
@@ -8,4 +8,4 @@
 if sys.version_info[:2] >= (3, 8):
     from cloudpickle.cloudpickle_fast import CloudPickler, dumps, dump
 
-__version__ = '1.2.3dev0'
+__version__ = '1.3.0dev0'
diff --git a/cloudpickle/cloudpickle.py b/cloudpickle/cloudpickle.py
index 638ec28ee..c48572323 100644
--- a/cloudpickle/cloudpickle.py
+++ b/cloudpickle/cloudpickle.py
@@ -95,7 +95,6 @@
     PY3 = False
     PY2 = True
 else:
-    types.ClassType = type
     from pickle import _Pickler as Pickler
     from io import BytesIO as StringIO
     string_types = (str,)
@@ -889,7 +888,8 @@ def save_global(self, obj, name=None, pack=struct.pack):
             Pickler.save_global(self, obj, name=name)
 
     dispatch[type] = save_global
-    dispatch[types.ClassType] = save_global
+    if PY2:
+        dispatch[types.ClassType] = save_global
 
     def save_instancemethod(self, obj):
         # Memoization rarely is ever useful due to python bounding