diff --git a/docs/topics/feed-exports.rst b/docs/topics/feed-exports.rst
index dee0c3ffa..cf70b8aca 100644
--- a/docs/topics/feed-exports.rst
+++ b/docs/topics/feed-exports.rst
@@ -312,7 +312,7 @@ The keys are URI schemes and the values are paths to storage classes.
 FEED_STORAGE_S3_ACL
 -------------------
 
-Default: ``None``
+Default: ``''`` (empty string)
 
 A string containing a custom ACL for feeds exported to Amazon S3 by your project.
 
diff --git a/scrapy/extensions/feedexport.py b/scrapy/extensions/feedexport.py
index 40f985f19..975fa1229 100644
--- a/scrapy/extensions/feedexport.py
+++ b/scrapy/extensions/feedexport.py
@@ -135,7 +135,7 @@ class S3FeedStorage(BlockingFeedStorage):
             uri=uri,
             access_key=crawler.settings['AWS_ACCESS_KEY_ID'],
             secret_key=crawler.settings['AWS_SECRET_ACCESS_KEY'],
-            acl=crawler.settings['FEED_STORAGE_S3_ACL']
+            acl=crawler.settings['FEED_STORAGE_S3_ACL'] or None
         )
 
     def _store_in_thread(self, file):
diff --git a/scrapy/settings/default_settings.py b/scrapy/settings/default_settings.py
index 776c5af23..a800d39ab 100644
--- a/scrapy/settings/default_settings.py
+++ b/scrapy/settings/default_settings.py
@@ -158,7 +158,7 @@ FEED_EXPORTERS_BASE = {
 }
 FEED_EXPORT_INDENT = 0
 
-FEED_STORAGE_S3_ACL = None
+FEED_STORAGE_S3_ACL = ''
 
 FILES_STORE_S3_ACL = 'private'
 FILES_STORE_GCS_ACL = ''