diff --git a/.github/workflows/r.yml b/.github/workflows/r.yml
index cf2e656..4a23475 100644
--- a/.github/workflows/r.yml
+++ b/.github/workflows/r.yml
@@ -38,7 +38,15 @@ jobs:
       - name: Set up R package dependencies
         uses: r-lib/actions/setup-r-dependencies@d3c5be51b12e724e68f33216ca3c148b66d5f0b6
         with:
-          extra-packages: any::rcmdcheck
+          # ponytail: RcppParallel 6.2.0 (oneTBB) broke the ABI of prebuilt
+          # qs2/stringfish binaries (undefined tbb::internal symbols). Build both
+          # from source and bust the package cache; drop these two refs and
+          # cache-version once CRAN/PPM binaries are rebuilt against 6.2.0.
+          cache-version: 2
+          extra-packages: |
+            any::rcmdcheck
+            stringfish=?source
+            qs2=?source
           needs: check
 
       - name: Run R CMD check