diff --git a/src/api/db/migrate/20170306105300_add_index_to_events.rb b/src/api/db/migrate/20170306105300_add_index_to_events.rb
new file mode 100644
index 00000000000..0370e2ce9cd
--- /dev/null
+++ b/src/api/db/migrate/20170306105300_add_index_to_events.rb
@@ -0,0 +1,9 @@
+class AddIndexToEvents < ActiveRecord::Migration
+  def self.up
+    add_index :events, :mails_sent
+  end
+
+  def self.down
+    remove_index :events, :mails_sent
+  end
+end
diff --git a/src/api/db/structure.sql b/src/api/db/structure.sql
index 0950c2447bd..879231f825c 100644
--- a/src/api/db/structure.sql
+++ b/src/api/db/structure.sql
@@ -481,7 +481,8 @@ CREATE TABLE `events` (
   KEY `index_events_on_queued` (`queued`),
   KEY `index_events_on_project_logged` (`project_logged`),
   KEY `index_events_on_eventtype` (`eventtype`),
-  KEY `index_events_on_created_at` (`created_at`)
+  KEY `index_events_on_created_at` (`created_at`),
+  KEY `index_events_on_mails_sent` (`mails_sent`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
 
 CREATE TABLE `flags` (
@@ -1402,6 +1403,7 @@ INSERT INTO schema_migrations (version) VALUES
 ('20170118091131'),
 ('20170123115500'),
 ('20170215231042'),
+('20170306105300'),
 ('21'),
 ('22'),
 ('23'),