diff --git a/roles/upload-logs-base/library/zuul_s3_upload.py b/roles/upload-logs-base/library/zuul_s3_upload.py
index 42990e681..8e7217ea9 100755
--- a/roles/upload-logs-base/library/zuul_s3_upload.py
+++ b/roles/upload-logs-base/library/zuul_s3_upload.py
@@ -38,6 +38,7 @@ import sys
 import threading
 
 import boto3
+import botocore
 from ansible.module_utils.basic import AnsibleModule
 
 try:
@@ -113,7 +114,13 @@ class Uploader():
             self.url = os.path.join(return_endpoint,
                                     self.prefix)
 
+        # The default for max_pool_connections is 10, which is easily
+        # exhausted if the upload threads overwhelm them.
+        client_config = botocore.config.Config(
+            max_pool_connections=MAX_UPLOAD_THREADS * 4)
+
         self.s3 = boto3.resource('s3',
+                                 config=client_config,
                                  endpoint_url=self.endpoint,
                                  **credential_args)
         self.bucket = self.s3.Bucket(bucket)