diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 17105b5..18257f7 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -21,6 +21,11 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Build package
+        env:
+          # Use the Tsinghua PyPI mirror for build-environment resolution;
+          # the self-hosted runner is in China and the default pypi.org is
+          # too slow / unreliable for build dependency install.
+          UV_DEFAULT_INDEX: "https://pypi.tuna.tsinghua.edu.cn/simple/"
         run: uv build
 
       - name: Upload wheel artifacts