diff --git a/.github/workflows/test_old_cpu.yml b/.github/workflows/test_old_cpu.yml
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+++ b/.github/workflows/test_old_cpu.yml
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+name: Test on Older CPUs (x86_64-v2)
+
+# This workflow tests numpy-quaddtype on older x86 CPUs using Intel SDE.
+# It ensures compatibility with x86_64-v2 baseline CPUs (e.g., Sandy Bridge)
+# that don't have AVX2/FMA support.
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  test_old_cpu:
+    name: Test on ${{ matrix.cpu[1] }}
+    runs-on: ubuntu-24.04
+    strategy:
+      fail-fast: false
+      matrix:
+        cpu:
+          - ['snb', 'Sandy Bridge (x86_64-v2)']
+          - ['hsw', 'Haswell (x86_64-v3)']
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          submodules: recursive
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: "3.12"
+
+      - name: Install Intel SDE
+        run: |
+          curl -o /tmp/sde.tar.xz https://downloadmirror.intel.com/859732/sde-external-9.58.0-2025-06-16-lin.tar.xz
+          mkdir /tmp/sde && tar -xvf /tmp/sde.tar.xz -C /tmp/sde/
+          sudo mv /tmp/sde/* /opt/sde && sudo ln -s /opt/sde/sde64 /usr/bin/sde
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update -y
+          sudo apt-get install -y cmake gcc g++ make git pkg-config
+
+      - name: Install Python dependencies
+        run: |
+          pip install -U pip
+          pip install numpy meson meson-python ninja pytest
+
+      - name: Build numpy-quaddtype
+        env:
+          LDFLAGS: "-fopenmp"
+        run: |
+          pip install . --no-build-isolation -v
+
+      - name: Test import on ${{ matrix.cpu[1] }}
+        run: |
+          echo "Testing basic import on ${{ matrix.cpu[1] }}..."
+          sde -${{ matrix.cpu[0] }} -- python -c "
+          import numpy as np
+          print('NumPy version:', np.__version__)
+          from numpy_quaddtype import QuadPrecDType
+          print('QuadPrecDType imported successfully!')
+          arr = np.zeros(3, dtype=QuadPrecDType())
+          print('Created quad array:', arr)
+          print('SUCCESS: Works on ${{ matrix.cpu[1] }}!')
+          "
+
+      - name: Run tests on ${{ matrix.cpu[1] }}
+        run: |
+          pip install pytest mpmath
+          sde -${{ matrix.cpu[0] }} -- python -m pytest tests/ -v --tb=short