diff --git a/ORE-SWIG/QuantExt-SWIG/SWIG/qle_common.i b/ORE-SWIG/QuantExt-SWIG/SWIG/qle_common.i
index 1ad9fe8f3f..68551d83a1 100644
--- a/ORE-SWIG/QuantExt-SWIG/SWIG/qle_common.i
+++ b/ORE-SWIG/QuantExt-SWIG/SWIG/qle_common.i
@@ -23,6 +23,18 @@
 #include <ql/optional.hpp>
 %}
 
+// SWIG registers its smart-pointer machinery under the bare namespace `ext`:
+// QuantLib-SWIG's common.i sets SWIG_SHARED_PTR_NAMESPACE to `ext`, and the C++
+// alias `namespace ext = QuantLib::ext` it relies on lives inside a %{ %} block
+// that the SWIG parser never sees.  A declaration spelled
+// `QuantLib::ext::shared_ptr<T>` is therefore registered as a type distinct from
+// `ext::shared_ptr<T>` and is wrapped as an opaque pointer instead of a proper
+// proxy, so a value produced by one spelling cannot be passed to the other -- for
+// example OREApp::getCube() to InputParameters::setCube().  Declaring the alias
+// where SWIG can see it collapses both spellings onto the same wrapped type.
+// See https://github.com/OpenSourceRisk/Engine/issues/351
+namespace QuantLib { namespace ext = ::ext; }
+
 
 #if defined(SWIGPYTHON)
 %typemap(in) boost::optional<bool> %{
diff --git a/ORE-SWIG/test/test_cube_reuse.py b/ORE-SWIG/test/test_cube_reuse.py
new file mode 100644
index 0000000000..f41dec35b9
--- /dev/null
+++ b/ORE-SWIG/test/test_cube_reuse.py
@@ -0,0 +1,59 @@
+"""Regression tests for https://github.com/OpenSourceRisk/Engine/issues/351.
+
+SWIG registers its smart-pointer machinery under the bare namespace ``ext``, so
+a declaration spelled ``QuantLib::ext::shared_ptr<T>`` used to be registered as
+a type distinct from ``ext::shared_ptr<T>`` and wrapped as an opaque pointer.
+Setters written with the qualified spelling then rejected every value the
+bindings could produce -- ``InputParameters.setCube`` could not be handed the
+cube returned by ``OREApp.getCube``, which made in-memory cube reuse
+unreachable from Python.
+"""
+
+import unittest
+
+import ORE
+
+
+class QualifiedSharedPtrSetterTest(unittest.TestCase):
+    """Setters declared with the qualified spelling must accept wrapped objects."""
+
+    #: Setters that take a qualified ``shared_ptr`` whose argument type can be
+    #: constructed directly from Python.
+    ENGINE_DATA_SETTERS = (
+        "setXvaSensiPricingEngine",
+        "setParConversionPricingEngine",
+        "setParStressPricingEngine",
+        "setZeroToParShiftPricingEngine",
+    )
+
+    def test_engine_data_setters_accept_a_wrapped_engine_data(self) -> None:
+        """These rejected every EngineData the bindings could produce."""
+        params = ORE.InputParameters()
+        for name in self.ENGINE_DATA_SETTERS:
+            if not hasattr(params, name):
+                continue  # setter predates this release
+            with self.subTest(setter=name):
+                getattr(params, name)(ORE.EngineData())
+
+    def test_set_cube_accepts_a_wrapped_cube(self) -> None:
+        """The round-trip issue #351 is about: hand a live cube to setCube.
+
+        Building the cube needs the in-memory cube classes to be concrete
+        (issue #354); where they are still abstract the round-trip cannot be
+        exercised and the test is skipped rather than failed.
+
+        setMarketCube is fixed by the same change but stays untested here:
+        AggregationScenarioData has no constructible subclass in the bindings.
+        """
+        asof = ORE.Date(2, ORE.March, 2026)
+        dates = [ORE.Date(2, ORE.March, 2027), ORE.Date(2, ORE.March, 2028)]
+        try:
+            cube = ORE.DoublePrecisionInMemoryCubeN(asof, {"trade1"}, dates, 4)
+        except AttributeError:
+            self.skipTest("in-memory cubes not constructible here (issue #354)")
+        params = ORE.InputParameters()
+        params.setCube(cube)
+
+
+if __name__ == "__main__":
+    unittest.main()