diff --git a/lib/fetch/body.js b/lib/fetch/body.js
index 3cb561c4478..b6dadce055c 100644
--- a/lib/fetch/body.js
+++ b/lib/fetch/body.js
@@ -434,16 +434,31 @@ function bodyMixinMethods (instance) {
         })
         busboy.on('file', (name, value, info) => {
           const { filename, encoding, mimeType } = info
-          const base64 = encoding.toLowerCase() === 'base64'
           const chunks = []
-          value.on('data', (chunk) => {
-            if (base64) chunk = Buffer.from(chunk.toString(), 'base64')
-            chunks.push(chunk)
-          })
-          value.on('end', () => {
-            const file = new File(chunks, filename, { type: mimeType })
-            responseFormData.append(name, file)
-          })
+
+          if (encoding.toLowerCase() === 'base64') {
+            let base64chunk = ''
+
+            value.on('data', (chunk) => {
+              base64chunk += chunk.toString().replace(/[\r\n]/gm, '')
+
+              const end = base64chunk.length - base64chunk.length % 4
+              chunks.push(Buffer.from(base64chunk.slice(0, end), 'base64'))
+
+              base64chunk = base64chunk.slice(end)
+            })
+            value.on('end', () => {
+              chunks.push(Buffer.from(base64chunk, 'base64'))
+              responseFormData.append(name, new File(chunks, filename, { type: mimeType }))
+            })
+          } else {
+            value.on('data', (chunk) => {
+              chunks.push(chunk)
+            })
+            value.on('end', () => {
+              responseFormData.append(name, new File(chunks, filename, { type: mimeType }))
+            })
+          }
         })
 
         const busboyResolve = new Promise((resolve, reject) => {
diff --git a/test/fetch/client-fetch.js b/test/fetch/client-fetch.js
index 5310f39a4c2..685e196276a 100644
--- a/test/fetch/client-fetch.js
+++ b/test/fetch/client-fetch.js
@@ -12,6 +12,7 @@ const nodeFetch = require('../../index-fetch')
 const { once } = require('events')
 const { gzipSync } = require('zlib')
 const { promisify } = require('util')
+const { randomFillSync, createHash } = require('crypto')
 
 setGlobalDispatcher(new Agent({
   keepAliveTimeout: 1,
@@ -200,10 +201,15 @@ test('multipart formdata base64', (t) => {
   t.plan(1)
 
   // Example form data with base64 encoding
-  const formRaw = '------formdata-undici-0.5786922755719377\r\nContent-Disposition: form-data; name="key"; filename="test.txt"\r\nContent-Type: text/plain\r\nContent-Transfer-Encoding: base64\r\n\r\ndmFsdWU=\r\n------formdata-undici-0.5786922755719377--'
-  const server = createServer((req, res) => {
+  const data = randomFillSync(Buffer.alloc(256))
+  const formRaw = `------formdata-undici-0.5786922755719377\r\nContent-Disposition: form-data; name="file"; filename="test.txt"\r\nContent-Type: application/octet-stream\r\nContent-Transfer-Encoding: base64\r\n\r\n${data.toString('base64')}\r\n------formdata-undici-0.5786922755719377--`
+  const server = createServer(async (req, res) => {
     res.setHeader('content-type', 'multipart/form-data; boundary=----formdata-undici-0.5786922755719377')
-    res.write(formRaw)
+
+    for (let offset = 0; offset < formRaw.length;) {
+      res.write(formRaw.slice(offset, offset += 2))
+      await new Promise(resolve => setTimeout(resolve))
+    }
     res.end()
   })
   t.teardown(server.close.bind(server))
@@ -211,9 +217,10 @@ test('multipart formdata base64', (t) => {
   server.listen(0, () => {
     fetch(`http://localhost:${server.address().port}`)
       .then(res => res.formData())
-      .then(form => form.get('key').text())
-      .then(text => {
-        t.equal(text, 'value')
+      .then(form => form.get('file').arrayBuffer())
+      .then(buffer => createHash('sha256').update(Buffer.from(buffer)).digest('base64'))
+      .then(digest => {
+        t.equal(createHash('sha256').update(data).digest('base64'), digest)
       })
   })
 })