diff --git a/lib/codegen/build.rs b/lib/codegen/build.rs
index 7e58b0d012..d127f357b4 100644
--- a/lib/codegen/build.rs
+++ b/lib/codegen/build.rs
@@ -50,7 +50,7 @@ fn main() {
     // The `build.py` script prints out its own dependencies.
     println!(
         "cargo:rerun-if-changed={}",
-        crate_dir.join("build.rs").to_string_lossy()
+        crate_dir.join("build.rs").to_str().unwrap()
     );
 
     // Scripts are in `$crate_dir/meta`.