diff --git a/build-libcxx.sh b/build-libcxx.sh
index a6bafd6..1def9e4 100755
--- a/build-libcxx.sh
+++ b/build-libcxx.sh
@@ -167,7 +167,7 @@ build_all() {
             -DLIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS=OFF \
             -DLLVM_NO_OLD_LIBSTDCXX=TRUE \
             -DCXX_SUPPORTS_CXX11=TRUE \
-            -DCMAKE_CXX_FLAGS="$LIBCXXABI_VISIBILITY_FLAGS -D_LIBCPP_HAS_THREAD_API_WIN32 -w" \
+            -DCMAKE_CXX_FLAGS="$LIBCXXABI_VISIBILITY_FLAGS -D_LIBCPP_HAS_THREAD_API_WIN32 -D_LIBCPP_ABI_UNSTABLE -w" \
             ..
         make -j$CORES
         cd ..