1 files changed, 10 insertions, 0 deletions
diff --git a/test/orm/test_merge.py b/test/orm/test_merge.py
index 8866223cc..0f29cfc56 100644
--- a/test/orm/test_merge.py
+++ b/test/orm/test_merge.py
@@ -31,10 +31,20 @@ from sqlalchemy.testing import not_in
 from sqlalchemy.testing.fixtures import fixture_session
 from sqlalchemy.testing.schema import Column
 from sqlalchemy.testing.schema import Table
+from sqlalchemy.util import has_compiled_ext
 from sqlalchemy.util import OrderedSet
 from test.orm import _fixtures
 
 
+if has_compiled_ext():
+    # cython ordered set is immutable, subclass it with a python
+    # class so that its method can be replaced
+    _OrderedSet = OrderedSet
+
+    class OrderedSet(_OrderedSet):
+        pass
+
+
 class MergeTest(_fixtures.FixtureTest):
     """Session.merge() functionality"""