diff --git a/lib/core/util.js b/lib/core/util.js
index ab397f89e74..dfefac6d15c 100644
--- a/lib/core/util.js
+++ b/lib/core/util.js
@@ -436,46 +436,6 @@ function parseHeaders (headers, obj) {
   return obj
 }
 
-function normalizeHeaders (headers) {
-  const ret = {}
-  if (headers == null) {
-    // Do nothing...
-  } else if (Array.isArray(headers)) {
-    for (let i = 0; i < headers.length; i += 2) {
-      if (Array.isArray(headers[i]) && headers[i].length === 2) {
-        const key = headerNameToString(headers[i][0])
-        const val = ret[key]
-        if (val == null) {
-          ret[key] = String(headers[i][1])
-        } else if (typeof val === 'string') {
-          ret[key] = [val, String(headers[i][1])]
-        } else {
-          val.push(String(headers[i][1]))
-        }
-      } else {
-        const key = headerNameToString(headers[i])
-        const val = ret[key]
-        if (val == null) {
-          ret[key] = String(headers[i + 1])
-        } else if (typeof val === 'string') {
-          ret[key] = [val, String(headers[i + 1])]
-        } else {
-          val.push(String(headers[i + 1]))
-        }
-      }
-    }
-  } else if (typeof headers[Symbol.iterator] === 'function') {
-    for (const [key, val] of headers) {
-      ret[headerNameToString(key)] = Array.isArray(val) ? val.map(x => String(x)) : String(val)
-    }
-  } else {
-    for (const [key, val] of Object.entries(headers)) {
-      ret[headerNameToString(key)] = Array.isArray(val) ? val.map(x => String(x)) : String(val)
-    }
-  }
-  return ret
-}
-
 /**
  * @param {Buffer[]} headers
  * @returns {string[]}
@@ -943,6 +903,5 @@ module.exports = {
   nodeMajor,
   nodeMinor,
   safeHTTPMethods: Object.freeze(['GET', 'HEAD', 'OPTIONS', 'TRACE']),
-  wrapRequestBody,
-  normalizeHeaders
+  wrapRequestBody
 }
diff --git a/lib/handler/redirect-handler.js b/lib/handler/redirect-handler.js
index c8c9d60663c..5a36318d89e 100644
--- a/lib/handler/redirect-handler.js
+++ b/lib/handler/redirect-handler.js
@@ -206,13 +206,26 @@ function shouldRemoveHeader (name, removeContent, unknownOrigin) {
 
 // https://tools.ietf.org/html/rfc7231#section-6.4
 function cleanRequestHeaders (headers, removeContent, unknownOrigin) {
-  const ret = util.normalizeHeaders(headers)
-  for (const name of Object.keys(ret)) {
-    if (shouldRemoveHeader(name, removeContent, unknownOrigin)) {
-      delete ret[name]
+  let ret
+  if (Array.isArray(headers)) {
+    for (let i = 0; i < headers.length; i += 2) {
+      const name = util.headerNameToString(headers[i])
+      if (!shouldRemoveHeader(name, removeContent, unknownOrigin)) {
+        ret ??= { ...headers }
+        ret[name] = headers[i + 1]
+      }
+    }
+  } else if (headers && typeof headers === 'object') {
+    const entries = typeof headers[Symbol.iterator] === 'function' ? headers : Object.entries(headers)
+    for (const [key, value] of entries) {
+      const name = util.headerNameToString(key)
+      if (!shouldRemoveHeader(name, removeContent, unknownOrigin)) {
+        ret ??= { ...headers }
+        ret[name] = value
+      }
     }
   }
-  return ret
+  return ret ?? headers
 }
 
 module.exports = RedirectHandler