diff --git a/lib/internal/http2/util.js b/lib/internal/http2/util.js
index 78ff2937c3a317..8a995cf003c75b 100644
--- a/lib/internal/http2/util.js
+++ b/lib/internal/http2/util.js
@@ -520,7 +520,7 @@ function mapToHeaders(map,
       err = assertValuePseudoHeader(key);
       if (err !== undefined)
         throw err;
-      ret = `${key}\0${value}\0${flags}${ret}`;
+      ret += `${key}\0${value}\0${flags}`;
       count++;
       continue;
     }