diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d89e2049..8bb1297c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -37,7 +37,12 @@ jobs:
         run: uv build --sdist --python=3.13
 
       - name: Install sdist from .tar.gz
-        run: python -m pip install dist/*.tar.gz
+        # XXX must install under py3.13 (matching the build's
+        # `--python=3.13`); the runner's default `python` is 3.12
+        # which our `requires-python = ">=3.13"` now rejects.
+        run: |
+          uv venv --python 3.13
+          uv pip install dist/*.tar.gz
 
   # ------ type-check ------
   # mypy: