diff --git a/src/listener.ts b/src/listener.ts
index d25f512..0215c29 100644
--- a/src/listener.ts
+++ b/src/listener.ts
@@ -53,12 +53,11 @@ const responseViaResponseObject = async (
   res: Response | Promise<Response>,
   outgoing: ServerResponse | Http2ServerResponse
 ) => {
-  if (res instanceof Promise) {
-    res = await res.catch(handleFetchError)
-  }
+  res = res instanceof Promise ? await res.catch(handleFetchError) : res
 
   try {
-    if (cacheKey in res) {
+    const isCached = cacheKey in res
+    if (isCached) {
       return responseViaCache(res as Response, outgoing)
     }
   } catch (e: unknown) {
@@ -77,20 +76,30 @@ const responseViaResponseObject = async (
        * Else if content-type is not application/json nor text/* but can be text/event-stream,
        * we assume that the response should be streamed.
        */
+
+      const {
+        'transfer-encoding': transferEncoding,
+        'content-encoding': contentEncoding,
+        'content-length': contentLength,
+        'x-accel-buffering': accelBuffering,
+        'content-type': contentType,
+      } = resHeaderRecord
+
       if (
-        resHeaderRecord['transfer-encoding'] ||
-        resHeaderRecord['content-encoding'] ||
-        resHeaderRecord['content-length'] ||
+        transferEncoding ||
+        contentEncoding ||
+        contentLength ||
         // nginx buffering variant
-        (resHeaderRecord['x-accel-buffering'] &&
-          regBuffer.test(resHeaderRecord['x-accel-buffering'] as string)) ||
-        !regContentType.test(resHeaderRecord['content-type'] as string)
+        (accelBuffering && regBuffer.test(accelBuffering as string)) ||
+        !regContentType.test(contentType as string)
       ) {
         outgoing.writeHead(res.status, resHeaderRecord)
+
         await writeFromReadableStream(res.body, outgoing)
       } else {
         const buffer = await res.arrayBuffer()
         resHeaderRecord['content-length'] = buffer.byteLength
+
         outgoing.writeHead(res.status, resHeaderRecord)
         outgoing.end(new Uint8Array(buffer))
       }
@@ -115,7 +124,9 @@ export const getRequestListener = (fetchCallback: FetchCallback) => {
     const req = newRequest(incoming)
 
     try {
-      res = fetchCallback(req, { incoming, outgoing } as HttpBindings) as Response | Promise<Response>
+      res = fetchCallback(req, { incoming, outgoing } as HttpBindings) as
+        | Response
+        | Promise<Response>
       if (cacheKey in res) {
         // synchronous, cacheable response
         return responseViaCache(res as Response, outgoing)