diff --git a/build.rs b/build.rs
index c72a2d4..d105ada 100644
--- a/build.rs
+++ b/build.rs
@@ -51,7 +51,7 @@ fn main() {
                .include("depend/secp256k1/include")
                .include("depend/secp256k1/src")
                .flag("-g")
-               .flag("-Wno-unused-function") // some ecmult stuff is defined but not used upstream
+               .flag_if_supported("-Wno-unused-function") // some ecmult stuff is defined but not used upstream
                .define("SECP256K1_BUILD", Some("1"))
                // TODO these three should be changed to use libgmp, at least until secp PR 290 is merged
                .define("USE_NUM_NONE", Some("1"))