diff --git a/setup.py b/setup.py
index b04cb1e9..b66a2b65 100644
--- a/setup.py
+++ b/setup.py
@@ -57,16 +57,18 @@ def build_extension(self, ext):
         cfg = "Debug" if self.debug else "Release"
         build_args = ["--config", cfg]
 
+        env = os.environ.copy()
+
         if platform.system() == "Windows":
             cmake_args += [f"-DCMAKE_LIBRARY_OUTPUT_DIRECTORY_{cfg.upper()}={extdir}"]
-            if sys.maxsize > 2 ** 32:
+            if sys.maxsize > 2**32:
                 cmake_args += ["-A", "x64"]
             build_args += ["--", "/m", "/p:TrackFileAccess=false"]
         else:
             cmake_args += ["-DCMAKE_BUILD_TYPE=" + cfg]
-            build_args += ["--", "-j"]
+            if "MAKEFLAGS" not in env:
+                build_args += ["--", "-j"]
 
-        env = os.environ.copy()
         env["CXXFLAGS"] = '{} -DVERSION_INFO=\\"{}\\"'.format(
             env.get("CXXFLAGS", ""), self.distribution.get_version()
         )
diff --git a/tenseal/cpp/tensors/encrypted_vector.h b/tenseal/cpp/tensors/encrypted_vector.h
index 9df2191e..19763539 100644
--- a/tenseal/cpp/tensors/encrypted_vector.h
+++ b/tenseal/cpp/tensors/encrypted_vector.h
@@ -186,28 +186,36 @@ class EncryptedVector : public EncryptedTensor<plain_t, encrypted_t> {
                 auto diag = matrix.get_diagonal(
                     -local_i,
                     this->tenseal_context()->template slot_count<encoder_t>());
-                replicate_vector(
-                    diag,
-                    this->tenseal_context()->template slot_count<encoder_t>());
-
-                rotate(diag.begin(), diag.begin() + diag.size() - local_i,
-                       diag.end());
-
-                this->tenseal_context()->template encode<encoder_t>(diag,
-                                                                    pt_diag);
 
-                if (this->_ciphertexts[0].parms_id() != pt_diag.parms_id()) {
-                    this->set_to_same_mod(pt_diag, _ciphertexts[0]);
+                // don't add zero diagonals to (a) improve performance and (b)
+                // avoid transparent ciphertext issues
+                bool is_diag_nonzero = std::any_of(
+                    diag.begin(), diag.end(), [](plain_t x) { return x != 0; });
+                if (is_diag_nonzero) {
+                    replicate_vector(diag,
+                                     this->tenseal_context()
+                                         ->template slot_count<encoder_t>());
+
+                    rotate(diag.begin(), diag.begin() + diag.size() - local_i,
+                           diag.end());
+
+                    this->tenseal_context()->template encode<encoder_t>(
+                        diag, pt_diag);
+
+                    if (this->_ciphertexts[0].parms_id() !=
+                        pt_diag.parms_id()) {
+                        this->set_to_same_mod(pt_diag, _ciphertexts[0]);
+                    }
+                    this->tenseal_context()->evaluator->multiply_plain(
+                        this->_ciphertexts[0], pt_diag, ct);
+
+                    this->tenseal_context()->evaluator->rotate_vector_inplace(
+                        ct, local_i, *this->tenseal_context()->galois_keys());
+
+                    // accumulate thread results
+                    this->tenseal_context()->evaluator->add_inplace(
+                        thread_result, ct);
                 }
-                this->tenseal_context()->evaluator->multiply_plain(
-                    this->_ciphertexts[0], pt_diag, ct);
-
-                this->tenseal_context()->evaluator->rotate_vector_inplace(
-                    ct, local_i, *this->tenseal_context()->galois_keys());
-
-                // accumulate thread results
-                this->tenseal_context()->evaluator->add_inplace(thread_result,
-                                                                ct);
             }
             return thread_result;
         };
diff --git a/tests/python/tenseal/tensors/test_ckks_tensor.py b/tests/python/tenseal/tensors/test_ckks_tensor.py
index 15011a0e..74984098 100644
--- a/tests/python/tenseal/tensors/test_ckks_tensor.py
+++ b/tests/python/tenseal/tensors/test_ckks_tensor.py
@@ -121,19 +121,39 @@ def test_reshape_batching(context, data, new_shape):
 @pytest.mark.parametrize(
     "data, slices, new_shape",
     [
-        ([0, 1, 2, 3, 4, 5], [slice(1, 4, None)], [3]),
-        ([0, 1, 2, 3, 4, 5], [slice(1, None, None)], [5]),
-        ([0, 1, 2, 3, 4, 5], [slice(None, 4, None)], [4]),
-        ([[0, 1, 2], [0, 1, 2], [0, 1, 2]], [slice(1, 3, None), slice(0, 2, None)], [2, 2]),
-        ([[0, 1, 2], [0, 1, 2], [0, 1, 2]], [slice(1, None, None), slice(0, 2, None)], [2, 2]),
+        ([0, 1, 2, 3, 4, 5], (slice(1, 4, None),), [3]),
+        ([0, 1, 2, 3, 4, 5], (slice(1, None, None),), [5]),
+        ([0, 1, 2, 3, 4, 5], (slice(None, 4, None),), [4]),
         (
             [[0, 1, 2], [0, 1, 2], [0, 1, 2]],
-            [slice(1, None, None), slice(None, None, None)],
+            (
+                slice(1, 3, None),
+                slice(0, 2, None),
+            ),
+            [2, 2],
+        ),
+        (
+            [[0, 1, 2], [0, 1, 2], [0, 1, 2]],
+            (
+                slice(1, None, None),
+                slice(0, 2, None),
+            ),
+            [2, 2],
+        ),
+        (
+            [[0, 1, 2], [0, 1, 2], [0, 1, 2]],
+            (
+                slice(1, None, None),
+                slice(None, None, None),
+            ),
             [2, 3],
         ),
         (
             [[0, 1, 2], [0, 1, 2], [0, 1, 2]],
-            [slice(None, None, None), slice(None, None, None)],
+            (
+                slice(None, None, None),
+                slice(None, None, None),
+            ),
             [3, 3],
         ),
         ([[0, 1, 2], [0, 1, 2], [0, 1, 2]], 1, [1, 3]),