diff --git a/__wasm/wit-bindgen-sample/container/src/fn_fetch.rs b/__wasm/wit-bindgen-sample/container/src/fn_fetch.rs
index 9babf55..d7ec35f 100644
--- a/__wasm/wit-bindgen-sample/container/src/fn_fetch.rs
+++ b/__wasm/wit-bindgen-sample/container/src/fn_fetch.rs
@@ -98,7 +98,7 @@ pub fn do_fetch(params: &str) -> FnResult {
     result_map.insert("status".to_string(), Value::Number(Number::from(status)));
     let mut headers_map = Map::new();
     for (k, v) in headers {
-        let header_key = k.map(|n| n.as_str().to_string()).unwrap_or_else(|| "".to_string());
+        let header_key = k.map(|n| n.as_str().to_string()).unwrap_or_else(|| "_".to_string());
         let header_value = match v.to_str() {
             Err(_) => continue,
             Ok(v) => v.to_string(),