diff --git a/lib/internal/v8_prof_polyfill.js b/lib/internal/v8_prof_polyfill.js
index 1bfa111d8d8ca3..5c6b1407120ea2 100644
--- a/lib/internal/v8_prof_polyfill.js
+++ b/lib/internal/v8_prof_polyfill.js
@@ -79,7 +79,7 @@ var line = '';
 
 function peekline() {
   const s = readline();
-  line = s + '\n' + line;
+  line = `${s}\n${line}`;
   return s;
 }