diff --git a/ia-upload-stream b/ia-upload-stream
index c40947c..a0a2d76 100755
--- a/ia-upload-stream
+++ b/ia-upload-stream
@@ -101,6 +101,19 @@ def readinto_size_limit(fin, fout, size, blockSize = 1048576):
 		size -= len(d)
 
 
+def get_part(f, partSize, progress):
+	data = io.BytesIO()
+	with maybe_file_progress_bar(progress, data, 'write', 'reading input') as w:
+		readinto_size_limit(f, w, partSize)
+	data.seek(0)
+	size = len(data.getbuffer())
+	logger.info('Calculating MD5')
+	h = hashlib.md5(data.getbuffer())
+	logger.info(f'MD5: {h.hexdigest()}')
+	contentMd5 = base64.b64encode(h.digest()).decode('ascii')
+	return (data, size, contentMd5)
+
+
 @contextlib.contextmanager
 def file_progress_bar(f, mode, description, size = None):
 	if size is None:
@@ -164,12 +177,14 @@ def maybe_file_progress_bar(progress, f, *args, **kwargs):
 
 def upload_one(url, uploadId, partNumber, data, contentMd5, size, headers, progress, tries, timeout):
 	r = None  # For UploadError in case of a timeout
+	if partNumber:
+		url = f'{url}?partNumber={partNumber}&uploadId={uploadId}'
 	for attempt in range(1, tries + 1):
 		if attempt > 1:
 			logger.info(f'Retrying part {partNumber}')
 		try:
 			with maybe_file_progress_bar(progress, data, 'read', f'uploading {partNumber}', size = size) as w:
-				r = requests.put(f'{url}?partNumber={partNumber}&uploadId={uploadId}', headers = {**headers, 'Content-MD5': contentMd5}, data = w, timeout = timeout)
+				r = requests.put(url, headers = {**headers, 'Content-MD5': contentMd5}, data = w, timeout = timeout)
 		except (ConnectionError, requests.exceptions.RequestException) as e:
 			err = f'error {type(e).__module__}.{type(e).__name__} {e!s}'
 		else:
@@ -208,12 +223,24 @@ def upload(item, filename, metadata, *, iaConfigFile = None, partSize = 100*1024
 
 	url = f'https://s3.us.archive.org/{item}/{filename}'
 	headers = {'Authorization': f'LOW {access}:{secret}'}
+	metadataHeaders = metadata_to_headers(metadata)
+	initialHeaders = {**headers, 'x-amz-auto-make-bucket': '1', **metadataHeaders}
+
+	# Always read the first part
+	data, size, contentMd5 = get_part(f, partSize, progress)
+
+	# If the file is only a single part anyway, use the normal PUT API instead of multipart because IA can process that *much* faster.
+	if uploadId is None and parts is None and complete and size < partSize:
+		logger.info(f'Uploading in one piece ({size} bytes)')
+		partNumber, eTag = upload_one(url, None, 0, data, contentMd5, size, initialHeaders, progress, tries, partTimeout)
+		logger.info(f'Upload OK, ETag: {eTag}')
+		logger.info('Done!')
+		return
 
 	if uploadId is None:
 		# Initiate multipart upload
 		logger.info(f'Initiating multipart upload for {filename} in {item}')
-		metadataHeaders = metadata_to_headers(metadata)
-		r = requests.post(f'{url}?uploads', headers = {**headers, 'x-amz-auto-make-bucket': '1', **metadataHeaders}, timeout = TIMEOUT)
+		r = requests.post(f'{url}?uploads', headers = initialHeaders, timeout = TIMEOUT)
 		if r.status_code != 200:
 			raise UploadError(f'Could not initiate multipart upload; got status {r.status_code} from IA S3', r = r)
 		# Fight me!
@@ -241,22 +268,18 @@ def upload(item, filename, metadata, *, iaConfigFile = None, partSize = 100*1024
 		parts = []
 	tasks = collections.deque()
 	with concurrent.futures.ThreadPoolExecutor(max_workers = concurrency) as executor:
-		for partNumber in itertools.count(start = len(parts) + 1):
+		logger.info(f'Uploading part {len(parts) + 1} ({size} bytes)')
+		task = executor.submit(upload_one, url, uploadId, len(parts) + 1, data, contentMd5, size, headers, progress, tries, partTimeout)
+		tasks.append(task)
+
+		for partNumber in itertools.count(start = len(parts) + 2):
 			while len(tasks) >= concurrency:
 				wait_first(tasks, parts)
-			data = io.BytesIO()
-			with maybe_file_progress_bar(progress, data, 'write', 'reading input') as w:
-				readinto_size_limit(f, w, partSize)
-			data.seek(0)
-			size = len(data.getbuffer())
+			data, size, contentMd5 = get_part(f, partSize, progress)
 			if not size:
 				# We're done!
 				break
 			logger.info(f'Uploading part {partNumber} ({size} bytes)')
-			logger.info('Calculating MD5')
-			h = hashlib.md5(data.getbuffer())
-			logger.info(f'MD5: {h.hexdigest()}')
-			contentMd5 = base64.b64encode(h.digest()).decode('ascii')
 
 			task = executor.submit(upload_one, url, uploadId, partNumber, data, contentMd5, size, headers, progress, tries, partTimeout)
 			tasks.append(task)