diff --git a/python/setup.py b/python/setup.py
index 9441d0e10d..f4ae508498 100755
--- a/python/setup.py
+++ b/python/setup.py
@@ -180,6 +180,7 @@ if __name__ == '__main__':
           'google.protobuf.descriptor_database',
           'google.protobuf.descriptor_pool',
           'google.protobuf.message_factory',
+          'google.protobuf.pyext.cpp_message',
           'google.protobuf.reflection',
           'google.protobuf.service',
           'google.protobuf.service_reflection',