diff --git a/tests/devices/default_tensor/test_scalability.py b/tests/devices/default_tensor/test_scalability.py
index 07eaef3c34f..010ccba776f 100644
--- a/tests/devices/default_tensor/test_scalability.py
+++ b/tests/devices/default_tensor/test_scalability.py
@@ -126,6 +126,7 @@ def circuit():
 
         _ = qml.QNode(circuit, dev)()
 
+    @pytest.mark.usefixtures("new_opmath_only")
     def test_hamiltonian(self, method):
         """Test that the device can compute the expval of a multi-qubit Hamiltonian."""
 
diff --git a/tests/ops/op_math/test_sum.py b/tests/ops/op_math/test_sum.py
index cf7ddf6f1ba..da611c32948 100644
--- a/tests/ops/op_math/test_sum.py
+++ b/tests/ops/op_math/test_sum.py
@@ -711,6 +711,7 @@ def test_eigendecompostion(self):
         assert np.allclose(eig_vals, true_eigvals)
         assert np.allclose(eig_vecs, true_eigvecs)
 
+    @pytest.mark.usefixtures("new_opmath_only")
     def test_eigendecomposition_repeat_operations(self):
         """Test that the eigendecomposition works with a repeated operation."""
         op1 = qml.X(0) + qml.X(0) + qml.X(0)