diff --git a/third_party/libcxx/__config_site b/third_party/libcxx/__config_site
index d99f4580e..82b354a8f 100644
--- a/third_party/libcxx/__config_site
+++ b/third_party/libcxx/__config_site
@@ -28,6 +28,7 @@ __static_yoink("__demangle");
 #define _LIBCPP_NO_ABI_TAG
 #define _LIBCPP_ABI_VERSION 2
 #define _LIBCPP_ABI_NAMESPACE __2
+#define _LIBCPP_USING_GETENTROPY
 #define _LIBCPP_DISABLE_AVAILABILITY
 #define _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS
 #define _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS