Index: libcxx/utils/ci/run-buildbot
===================================================================
--- libcxx/utils/ci/run-buildbot
+++ libcxx/utils/ci/run-buildbot
@@ -83,6 +83,7 @@
           -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
           -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+          -DLIBCXX_ENABLE_WERROR=YES \
           -DLLVM_LIT_ARGS="-sv --show-unsupported --xunit-xml-output test-results.xml" \
           "${@}"
 }