diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -79,6 +79,7 @@
           -DLLVM_ENABLE_PROJECTS="libcxx;libunwind;libcxxabi" \
           -DLLVM_LIT_ARGS="-sv --show-unsupported --xunit-xml-output test-results.xml" \
           -DLIBCXX_CXX_ABI=libcxxabi \
+          -DLIBCXX_TEST_CONFIG="${MONOREPO_ROOT}/libcxx/test/configs/libcxx-trunk-shared.cfg.in" \
           "${@}"
 }
 
@@ -301,9 +302,12 @@
 
     export CC=clang
     export CXX=clang++
+    # TODO: In the future, we should create a minimal testing config for back-deployment
+    #       and use that instead of the legacy config.
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Apple.cmake" \
                    -DLIBCXX_TEST_PARAMS="${PARAMS}" \
-                   -DLIBCXXABI_TEST_PARAMS="${PARAMS}"
+                   -DLIBCXXABI_TEST_PARAMS="${PARAMS}" \
+                   -DLIBCXX_TEST_CONFIG="${MONOREPO_ROOT}/libcxx/test/configs/legacy.cfg.in" \
 
     # TODO: Also run the libc++abi tests
     echo "+++ Running the libc++ tests"