diff --git a/.gitea/workflows/cpp-tests.yml b/.gitea/workflows/cpp-tests.yml
index 36b142a..84a4396 100644
--- a/.gitea/workflows/cpp-tests.yml
+++ b/.gitea/workflows/cpp-tests.yml
@@ -41,7 +41,11 @@ jobs:
         run: cmake -S code -B build -DCMAKE_BUILD_TYPE=Release
 
       - name: Build
-        run: nice -n 19 cmake --build build --target conformallab_tests -j$(nproc)
+        # Serial build (-j1): the 800m-limited container OOM-kills cc1plus when
+        # several Eigen+GoogleTest translation units compile in parallel
+        # (`-j$(nproc)`), failing test-fast non-deterministically regardless of
+        # branch content.  Mirrors the Pi-protection already used by test-cgal.
+        run: nice -n 19 cmake --build build --target conformallab_tests -j1
 
       - name: Run tests
         run: >