diff --git a/.gitignore b/.gitignore
index 5edef95..3c2e0ba 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 /target/
 /Cargo.lock
 /bad.wasm
+/bad.js
 /bad.wat
 /wabt*
 /js/
diff --git a/src/targets/wasm.rs b/src/targets/wasm.rs
index 0eb6508..a3b124e 100644
--- a/src/targets/wasm.rs
+++ b/src/targets/wasm.rs
@@ -1357,7 +1357,7 @@ mod tests {
         let ir: IrProject = proj.into();
         let wasm: WebWasmFile = ir.into();
         fs::write("./bad.wasm", wasm.wasm_bytes()).expect("failed to write to bad.wasm");
-        fs::write("./bad.js", wasm.js_string()).expect("failed to write to bad.js");
+        fs::write("./bad.mjs", format!("export default {};", wasm.js_string())).expect("failed to write to bad.js");
         let output = Command::new("node")
             .arg("-e")
             .arg(format!("({})().catch(console.error)", wasm.js_string()))