--- a/buildtools/third_party/libc++/__config_site
+++ b/buildtools/third_party/libc++/__config_site
@@ -25,7 +25,7 @@
 #define _LIBCPP_HAS_THREADS 1
 #define _LIBCPP_HAS_MONOTONIC_CLOCK 1
 #define _LIBCPP_HAS_TERMINAL 1
-#define _LIBCPP_HAS_MUSL_LIBC 0
+#define _LIBCPP_HAS_MUSL_LIBC 1
 
 #ifdef _WIN32
 #define _LIBCPP_HAS_THREAD_API_PTHREAD 0
