diff --git a/build.rs b/build.rs
index a08cc24..0704fa3 100644
--- a/build.rs
+++ b/build.rs
@@ -29,7 +29,6 @@ fn main() {
 fn setup_compiler_flags(build: &mut cc::Build) {
     build
         .static_flag(true)
-        .flag("-O3")
         .flag("-fno-builtin-printf")
         .flag("-fno-builtin-memcmp")
         .flag("-nostdinc")
@@ -63,12 +62,12 @@ fn setup_compiler_flags(build: &mut cc::Build) {
         //     build.flag("-g").flag("-fno-omit-frame-pointer");
         // }
 
-        // let opt_level = env::var("OPT_LEVEL").expect("fetching OPT_LEVEL");
-        // if opt_level == "z" {
-        //     build.flag("-Os");
-        // } else {
-        //     build.flag(&format!("-O{}", opt_level));
-        // }
+        let opt_level = env::var("OPT_LEVEL").expect("fetching OPT_LEVEL");
+        if opt_level == "z" {
+            build.flag("-Os");
+        } else {
+            build.flag(&format!("-O{}", opt_level));
+        }
     } else if compiler.is_like_gnu() {
         build
             .flag("-nostartfiles")