diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e7f643078..d540667f6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -157,7 +157,12 @@ jobs:
       - name: build + test
         uses: ./.github/actions/multi-functest
         with:
-          nix-shell: 'ci'
+          # clang 22 shell: the default `ci` shell's clang 21 ASan runtime
+          # deadlocks at process startup on the macos-latest / macOS 26 (Tahoe)
+          # image (compiler-rt shadow-memory init; same symptom as
+          # python/cpython#145199), fixed in LLVM >= 22 by
+          # llvm/llvm-project#191039 (backport #192082).
+          nix-shell: 'clang22'
           nix-cache: 'false'
           gh_token: ${{ secrets.GITHUB_TOKEN }}
           compile_mode: 'native'