diff --git a/src/context.ts b/src/context.ts
index 7acab14f..a23942e0 100644
--- a/src/context.ts
+++ b/src/context.ts
@@ -266,7 +266,10 @@ export const TEXT_PLAIN = 'text/plain; charset=UTF-8'
  * @returns The updated Headers object.
  */
 const setHeaders = (headers: Headers, map: Record<string, string> = {}) => {
-  Object.entries(map).forEach(([key, value]) => headers.set(key, value))
+  for (let i = 0, keys = Object.keys(map), len = keys.length; i < len; i++) {
+    const key = keys[i]
+    headers.set(key, map[key])
+  }
   return headers
 }