diff --git a/db/migrate/20150630071537_add_index_on_replies_msisdn_discovery_id.rb b/db/migrate/20150630071537_add_index_on_replies_msisdn_discovery_id.rb
new file mode 100644
index 0000000..b1f3ecf
--- /dev/null
+++ b/db/migrate/20150630071537_add_index_on_replies_msisdn_discovery_id.rb
@@ -0,0 +1,5 @@
+class AddIndexOnRepliesMsisdnDiscoveryId < ActiveRecord::Migration
+  def change
+    add_index(:replies, :msisdn_discovery_id)
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index e33c746..a8c4550 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20150607062339) do
+ActiveRecord::Schema.define(version: 20150630071537) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -177,6 +177,7 @@
   end
 
   add_index "replies", ["chat_id"], name: "index_replies_on_chat_id", using: :btree
+  add_index "replies", ["msisdn_discovery_id"], name: "index_replies_on_msisdn_discovery_id", using: :btree
   add_index "replies", ["state"], name: "index_replies_on_state", using: :btree
   add_index "replies", ["token"], name: "index_replies_on_token", unique: true, using: :btree
   add_index "replies", ["user_id"], name: "index_replies_on_user_id", using: :btree