diff --git a/lib/handler/cache-handler.js b/lib/handler/cache-handler.js
index e02ff9c9d72..44b82c4a9bb 100644
--- a/lib/handler/cache-handler.js
+++ b/lib/handler/cache-handler.js
@@ -4,7 +4,8 @@ const util = require('../core/util')
 const {
   parseCacheControlHeader,
   parseVaryHeader,
-  isEtagUsable
+  isEtagUsable,
+  makeHeaderNamesLowercase
 } = require('../util/cache')
 const { parseHttpDate } = require('../util/date.js')
 
@@ -96,7 +97,7 @@ class CacheHandler {
         statusMessage
       )
 
-    if (
+      if (
       !util.safeHTTPMethods.includes(this.#cacheKey.method) &&
       statusCode >= 200 &&
       statusCode <= 399
@@ -115,7 +116,7 @@ class CacheHandler {
     const heuristicallyCacheable = resHeaders['last-modified'] && HEURISTICALLY_CACHEABLE_STATUS_CODES.includes(statusCode)
     if (
       !cacheControlHeader &&
-      !resHeaders['expires'] &&
+      !resHeaders.expires &&
       !heuristicallyCacheable &&
       !this.#cacheByDefault
     ) {
@@ -157,6 +158,7 @@ class CacheHandler {
     let varyDirectives
     if (this.#cacheKey.headers && resHeaders.vary) {
       varyDirectives = parseVaryHeader(resHeaders.vary, this.#cacheKey.headers)
+
       if (!varyDirectives) {
         // Parse error
         return downstreamOnHeaders()
diff --git a/lib/interceptor/cache.js b/lib/interceptor/cache.js
index 6d1225680e7..84ae3646cbc 100644
--- a/lib/interceptor/cache.js
+++ b/lib/interceptor/cache.js
@@ -318,7 +318,7 @@ module.exports = (opts = {}) => {
         // Not a method we want to cache or we don't have the origin, skip
         return dispatch(opts, handler)
       }
-
+console.log('reqHeaders=', opts.headers)
       const reqCacheControl = opts.headers?.['cache-control']
         ? parseCacheControlHeader(opts.headers['cache-control'])
         : undefined
diff --git a/lib/util/cache.js b/lib/util/cache.js
index 35c53512b2a..175f9cfe49a 100644
--- a/lib/util/cache.js
+++ b/lib/util/cache.js
@@ -38,7 +38,7 @@ function makeCacheKey (opts) {
     origin: opts.origin.toString(),
     method: opts.method,
     path: opts.path,
-    headers
+    headers: makeHeaderNamesLowercase(headers)
   }
 }
 
@@ -347,6 +347,20 @@ function assertCacheMethods (methods, name = 'CacheMethods') {
   }
 }
 
+/**
+ * @param {import('../../types/header.d.ts').IncomingHttpHeaders} headers
+ * @returns {import('../../types/header.d.ts').IncomingHttpHeaders}
+ */
+function makeHeaderNamesLowercase (headers) {
+  const lowercased = {}
+
+  for (const header of Object.keys(headers)) {
+    lowercased[header.toLowerCase()] = headers[header]
+  }
+
+  return lowercased
+}
+
 module.exports = {
   makeCacheKey,
   assertCacheKey,
@@ -355,5 +369,6 @@ module.exports = {
   parseVaryHeader,
   isEtagUsable,
   assertCacheMethods,
-  assertCacheStore
+  assertCacheStore,
+  makeHeaderNamesLowercase
 }
diff --git a/test/interceptors/cache.js b/test/interceptors/cache.js
index dc120c60b7b..9a77fa1600f 100644
--- a/test/interceptors/cache.js
+++ b/test/interceptors/cache.js
@@ -128,6 +128,51 @@ describe('Cache Interceptor', () => {
     }
   })
 
+  test('vary directives are case-insensitive', async () => {
+    let requestsToOrigin = 0
+    const server = createServer((_, res) => {
+      requestsToOrigin++
+
+      res.setHeader('date', 0)
+      res.setHeader('cache-control', 'max-age=5000')
+      res.setHeader('vary', 'FoO, bar, bAZ')
+
+      res.end('asd')
+    }).listen(0)
+
+    const client = new Client(`http://localhost:${server.address().port}`)
+      .compose(interceptors.cache())
+
+    after(async () => {
+      server.close()
+      await client.close()
+    })
+
+    await once(server, 'listening')
+
+    strictEqual(requestsToOrigin, 0)
+
+    /**
+     * @type {import('../../types/dispatcher').default.RequestOptions}
+     */
+    const request = {
+      origin: 'localhost',
+      method: 'GET',
+      path: '/',
+      headers: {
+        Foo: '1',
+        BAr: 'abc',
+        BAZ: '789'
+      }
+    }
+
+    await client.request(request)
+    equal(requestsToOrigin, 1)
+
+    await client.request(request)
+    equal(requestsToOrigin, 1)
+  })
+
   test('stale responses are revalidated before deleteAt (if-modified-since)', async () => {
     const clock = FakeTimers.install({
       shouldClearNativeTimers: true
diff --git a/tmp.mjs b/tmp.mjs
new file mode 100644
index 00000000000..534c8035a17
--- /dev/null
+++ b/tmp.mjs
@@ -0,0 +1,5 @@
+import { Client, interceptors }  from './index.js'
+
+const client = new Client('https://google.com').compose(interceptors.cache())
+
+await client.request({ path: '/', method: 'GET', origin: 'google.com' })