diff --git a/lib/searchkick/query.rb b/lib/searchkick/query.rb
index 0aca7a2..41afb08 100644
--- a/lib/searchkick/query.rb
+++ b/lib/searchkick/query.rb
@@ -519,6 +519,12 @@ module Searchkick
       # run block
       options[:block].call(payload) if options[:block]
 
+      # scroll optimization when interating over all docs
+      # https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-scroll.html
+      if options[:scroll] && payload[:query] == {match_all: {}}
+        payload[:sort] ||= ["_doc"]
+      end
+
       @body = payload
       @page = page
       @per_page = per_page
--
libgit2 0.21.0