diff --git a/decnumber-sys/build.rs b/decnumber-sys/build.rs
index 81ed464..14816cc 100644
--- a/decnumber-sys/build.rs
+++ b/decnumber-sys/build.rs
@@ -17,6 +17,7 @@ fn main() {
     };
     cc::Build::new()
         .define("DECLITEND", Some(declitend))
+        .flag_if_supported("-O3")
         .file("decnumber/decimal128.c")
         .file("decnumber/decimal64.c")
         .file("decnumber/decimal32.c")