diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d28011b..68d9c54 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,6 +26,7 @@ jobs:
       - name: Install dev dependencies
         run: |
           python -m pip install --upgrade pip
+          pip install "numpy<2.5.0"
           pip install -e ".[dev]"
 
       - name: ruff check
@@ -60,6 +61,7 @@ jobs:
       - name: Install package
         run: |
           python -m pip install --upgrade pip
+          pip install "numpy<2.5.0"
           pip install -e ".[dev]"
 
       - name: Run tests
diff --git a/snapvec/_index.py b/snapvec/_index.py
index fdc793e..b4c95f9 100644
--- a/snapvec/_index.py
+++ b/snapvec/_index.py
@@ -303,7 +303,8 @@ def add_batch(self, ids: list[Any], vectors: NDArray[np.float32]) -> None:
             reconstructed: NDArray[np.float32] = self._centroids[batch_idx]
             r_scaled: NDArray[np.float32] = scaled - reconstructed
             # sign(S·r_rot) = sign(S·r_scaled) — scale-invariant
-            S_r: NDArray[np.float32] = (self._S @ r_scaled.T).T
+            # Optimized: r_scaled @ S.T is faster and avoids intermediate F-contiguous views
+            S_r: NDArray[np.float32] = r_scaled @ self._S.T
             qjl_signs = np.sign(S_r).astype(np.int8)
             qjl_signs[qjl_signs == 0] = 1
             # Store ‖r_rot‖ = ‖r_scaled‖/√pdim (unscaled space norm)