diff --git a/curl-sys/build.rs b/curl-sys/build.rs
index 9d416f189a..d403466ff7 100644
--- a/curl-sys/build.rs
+++ b/curl-sys/build.rs
@@ -242,6 +242,7 @@ fn main() {
         if cfg!(feature = "ssl") {
             if target.contains("-apple-") {
                 cfg.define("USE_DARWINSSL", None)
+                    .define("HAVE_BUILTIN_AVAILABLE", "1")
                     .file("curl/lib/vtls/darwinssl.c");
             } else {
                 cfg.define("USE_OPENSSL", None)