diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bcd03ca..e1105c5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -40,7 +40,11 @@ jobs:
       - uses: astral-sh/setup-uv@1c37ad07a6a961277cf70c0d37d6f313000f5884 # v10.3.0
         with:
           python-version: ${{ matrix.python-version }}
-      - run: uv run pytest
+      - name: Test without numpy
+        run: uv run pytest
+      # numpy is opt-in (use_numpy_arrays=True), so this second run covers both code paths.
+      - name: Test with numpy
+        run: uv run --extra numpy pytest
 
   build:
     runs-on: ubuntu-latest
diff --git a/README.md b/README.md
index ddec2e9..76ea705 100644
--- a/README.md
+++ b/README.md
@@ -190,6 +190,7 @@ From a clone of the GitHub repository, run the tests and the linter with [uv](ht
 
 ```sh
 uv run pytest
+uv run --extra numpy pytest  # also runs the numpy array tests
 uv run ruff check
 ```