diff --git a/mozjs-sys/build.rs b/mozjs-sys/build.rs
index 20466425dec..ebd3c768400 100644
--- a/mozjs-sys/build.rs
+++ b/mozjs-sys/build.rs
@@ -331,7 +331,7 @@ fn build_jsapi_bindings(build_dir: &Path) {
         builder = builder.clang_arg("-fms-compatibility");
     }
 
-    if let Ok(flags) = env::var("CXXFLAGS") {
+    if let Ok(flags) = env::var("BINDGEN_CXXFLAGS") {
         for flag in flags.split_whitespace() {
             builder = builder.clang_arg(flag);
         }