diff --git a/lib/logstash/outputs/elasticsearch/http_client.rb b/lib/logstash/outputs/elasticsearch/http_client.rb
index 32a37e82a..e02f692bd 100644
--- a/lib/logstash/outputs/elasticsearch/http_client.rb
+++ b/lib/logstash/outputs/elasticsearch/http_client.rb
@@ -12,16 +12,15 @@ module LogStash; module Outputs; class ElasticSearch;
   # there really isn't a good reason to configure it.
   #
   # The criteria used are:
-  # 1. We need a number that's less than 100MiB because ES
-  #    won't accept bulks larger than that.
+  # 1. We need a number that's less than 10MiB because ES is commonly
+  #    configured (particular in AWS Elasticsearch Service) to not
+  #    accept bulks larger than that.
   # 2. It must be large enough to amortize the connection constant
   #    across multiple requests.
   # 3. It must be small enough that even if multiple threads hit this size
   #    we won't use a lot of heap.
   #
-  # We wound up agreeing that a number greater than 10 MiB and less than 100MiB
-  # made sense. We picked one on the lowish side to not use too much heap.
-  TARGET_BULK_BYTES = 20 * 1024 * 1024 # 20MiB
+  TARGET_BULK_BYTES = 9 * 1024 * 1024 # 9MiB
 
   class HttpClient
     attr_reader :client, :options, :logger, :pool, :action_count, :recv_count