diff --git a/packages/core/src/highlevel/methods/files/download-stream.ts b/packages/core/src/highlevel/methods/files/download-stream.ts
index f4fdf277..54743072 100644
--- a/packages/core/src/highlevel/methods/files/download-stream.ts
+++ b/packages/core/src/highlevel/methods/files/download-stream.ts
@@ -1,12 +1,11 @@
 import type { ITelegramClient } from '../../client.types.js'
 import type { FileDownloadLocation, FileDownloadParameters } from '../../types/index.js'
 import { FileLocation } from '../../types/index.js'
-import { bufferToStream } from '../../utils/stream-utils.js'
 
 import { downloadAsIterable } from './download-iterable.js'
 
 /**
- * Download a file and return it as a readable stream,
+ * Download a file and return it as a `@fuman/io` stream,
  * streaming file contents.
  *
  * @param params  File download parameters
@@ -17,7 +16,13 @@ export function downloadAsStream(
     params?: FileDownloadParameters,
 ): ReadableStream<Uint8Array> {
     if (location instanceof FileLocation && ArrayBuffer.isView(location.location)) {
-        return bufferToStream(location.location)
+        const buf = location.location
+        return new ReadableStream({
+            start(controller) {
+                controller.enqueue(buf)
+                controller.close()
+            },
+        })
     }
 
     const cancel = new AbortController()
diff --git a/packages/core/src/highlevel/methods/files/upload-file.ts b/packages/core/src/highlevel/methods/files/upload-file.ts
index 2b585cfe..4c633120 100644
--- a/packages/core/src/highlevel/methods/files/upload-file.ts
+++ b/packages/core/src/highlevel/methods/files/upload-file.ts
@@ -1,6 +1,6 @@
 import type { tl } from '@mtcute/tl'
 import type { IReadable } from '@fuman/io'
-import { read, webReadableToFuman } from '@fuman/io'
+import { Bytes, read, webReadableToFuman } from '@fuman/io'
 import { AsyncLock } from '@fuman/utils'
 
 import { MtArgumentError } from '../../../types/errors.js'
@@ -9,7 +9,6 @@ import type { ITelegramClient } from '../../client.types.js'
 import type { UploadFileLike, UploadedFile } from '../../types/index.js'
 import { MIME_TO_EXTENSION, guessFileMime } from '../../utils/file-type.js'
 import { determinePartSize, isProbablyPlainText } from '../../utils/file-utils.js'
-import { bufferToStream } from '../../utils/stream-utils.js'
 
 const OVERRIDE_MIME: Record<string, string> = {
     // tg doesn't interpret `audio/opus` files as voice messages for some reason
@@ -131,7 +130,7 @@ export async function uploadFile(
 
     if (ArrayBuffer.isView(file)) {
         fileSize = file.length
-        file = bufferToStream(file)
+        file = Bytes.from(file)
     }
 
     if (HAS_FILE && file instanceof File) {
@@ -190,7 +189,7 @@ export async function uploadFile(
         throw new MtArgumentError('Could not convert input `file` to stream!')
     }
 
-    const readable = file as IReadable
+    let readable = file as IReadable
 
     // set file size if not automatically inferred
     if (fileSize === -1 && params.fileSize) fileSize = params.fileSize
@@ -199,7 +198,7 @@ export async function uploadFile(
         // buffer the entire stream in memory, then convert it back to stream (bruh)
         const buffer = await read.async.untilEnd(readable)
         fileSize = buffer.length
-        file = bufferToStream(buffer)
+        readable = Bytes.from(buffer)
     }
 
     let partSizeKb = params.partSize
@@ -245,11 +244,18 @@ export async function uploadFile(
 
     let pos = 0
     let idx = 0
+    let readableEnded = false
 
     const uploadNextPart = async (): Promise<void> => {
         const thisIdx = idx++
 
         await lock.acquire()
+
+        if (readableEnded) {
+            lock.release()
+            return
+        }
+
         let part
         try {
             part = await read.async.exactly(readable, partSize, 'truncate')
@@ -258,14 +264,16 @@ export async function uploadFile(
         }
 
         const ended = part.length < partSize
+        if (ended) {
+            readableEnded = true
 
-        if (ended && fileSize !== -1 && thisIdx !== partCount - 1) {
-            throw new MtArgumentError(`Unexpected EOS (there were only ${idx} parts, but expected ${partCount})`)
-        }
+            if (fileSize === -1) {
+                fileSize = pos + part.length
+                partCount = ~~((fileSize + partSize - 1) / partSize)
+            } else if (thisIdx !== partCount - 1) {
+                throw new MtArgumentError(`Unexpected EOS (there were only ${idx} parts, but expected ${partCount})`)
+            }
 
-        if (ended && fileSize === -1) {
-            fileSize = pos + part.length
-            partCount = ~~((fileSize + partSize - 1) / partSize)
             client.log.debug('readable ended, file size = %d, part count = %d', fileSize, partCount)
         }
 
diff --git a/packages/core/src/highlevel/utils/stream-utils.ts b/packages/core/src/highlevel/utils/stream-utils.ts
index e8c11cbb..47f42a06 100644
--- a/packages/core/src/highlevel/utils/stream-utils.ts
+++ b/packages/core/src/highlevel/utils/stream-utils.ts
@@ -1,14 +1,5 @@
 import { u8 } from '@fuman/utils'
 
-export function bufferToStream(buf: Uint8Array): ReadableStream<Uint8Array> {
-    return new ReadableStream({
-        start(controller) {
-            controller.enqueue(buf)
-            controller.close()
-        },
-    })
-}
-
 export async function streamToBuffer(stream: ReadableStream<Uint8Array>): Promise<Uint8Array> {
     const chunks: Uint8Array[] = []