diff --git a/sendsafely/utilities.py b/sendsafely/utilities.py
index a7d9a7b..346abb2 100644
--- a/sendsafely/utilities.py
+++ b/sendsafely/utilities.py
@@ -15,6 +15,8 @@
 import json
 import os
 import secrets
+import sys
+import time
 
 import requests
 from .pgpy import PGPMessage, PGPKey
@@ -195,7 +197,21 @@ def _upload_file_part_to_s3(encrypted_file_part, url):
     :param url: The S3 URL we're uploading to
     :return: The JSON response from S3.
     """
-    return requests.put(url=url, data=encrypted_file_part)
+    max_attempts = 5
+    max_backoff_seconds = 180
+    for attempt in range(max_attempts):
+        try:
+            return requests.put(url=url, data=encrypted_file_part)
+        except (requests.exceptions.ConnectionError, requests.exceptions.Timeout,
+                requests.exceptions.ChunkedEncodingError) as e:
+            if attempt == max_attempts - 1:
+                raise
+            sleep_seconds = min(2 ** attempt, max_backoff_seconds)
+            sys.stdout.write(
+                '\nRetrying S3 part upload (attempt {0}/{1}) after {2}: sleeping {3}s\n'.format(
+                    attempt + 2, max_attempts, type(e).__name__, sleep_seconds))
+            sys.stdout.flush()
+            time.sleep(sleep_seconds)
 
 
 def _calculate_package_checksum(package_code, keycode):
@@ -333,4 +349,4 @@ def _make_safe_for_urlsafebase64(client_secret):
     client_secret = client_secret.replace("=", "")
     client_secret = client_secret.replace("+", "-")
     client_secret = client_secret.replace("/", "_")
-    return client_secret
\ No newline at end of file
+    return client_secret