diff --git a/lib/fetch/body.js b/lib/fetch/body.js
index c291afa9368..db450ee6bd4 100644
--- a/lib/fetch/body.js
+++ b/lib/fetch/body.js
@@ -123,6 +123,7 @@ function extractBody (object, keepalive = false) {
     const blobParts = []
     const rn = new Uint8Array([13, 10]) // '\r\n'
     length = 0
+    let hasUnknownSizeValue = false
 
     for (const [name, value] of object) {
       if (typeof value === 'string') {
@@ -138,13 +139,20 @@ function extractBody (object, keepalive = false) {
             value.type || 'application/octet-stream'
           }\r\n\r\n`)
         blobParts.push(chunk, value, rn)
-        length += chunk.byteLength + value.size + rn.byteLength
+        if (typeof value.size === 'number') {
+          length += chunk.byteLength + value.size + rn.byteLength
+        } else {
+          hasUnknownSizeValue = true
+        }
       }
     }
 
     const chunk = enc.encode(`--${boundary}--`)
     blobParts.push(chunk)
     length += chunk.byteLength
+    if (hasUnknownSizeValue) {
+      length = null
+    }
 
     // Set source to object.
     source = object
diff --git a/test/issue-2065.js b/test/issue-2065.js
index 84183f0fb7c..cc288c48a74 100644
--- a/test/issue-2065.js
+++ b/test/issue-2065.js
@@ -4,6 +4,7 @@ const { test, skip } = require('tap')
 const { nodeMajor, nodeMinor } = require('../lib/core/util')
 const { createServer } = require('http')
 const { once } = require('events')
+const { createReadStream } = require('fs')
 const { File, FormData, request } = require('..')
 
 if (nodeMajor < 16 || (nodeMajor === 16 && nodeMinor < 8)) {
@@ -28,3 +29,43 @@ test('undici.request with a FormData body should set content-length header', asy
     body
   })
 })
+
+test('undici.request with a FormData stream value should set transfer-encoding header', async (t) => {
+  const server = createServer((req, res) => {
+    t.equal(req.headers['transfer-encoding'], 'chunked')
+    res.end()
+  }).listen(0)
+
+  t.teardown(server.close.bind(server))
+  await once(server, 'listening')
+
+  class BlobFromStream {
+    #stream
+    #type
+    constructor (stream, type) {
+      this.#stream = stream
+      this.#type = type
+    }
+
+    stream () {
+      return this.#stream
+    }
+
+    get type () {
+      return this.#type
+    }
+
+    get [Symbol.toStringTag] () {
+      return 'Blob'
+    }
+  }
+
+  const body = new FormData()
+  const fileReadable = createReadStream(__filename)
+  body.set('file', new BlobFromStream(fileReadable, '.js'), 'streamfile')
+
+  await request(`http://localhost:${server.address().port}`, {
+    method: 'POST',
+    body
+  })
+})