diff --git a/Gemfile b/Gemfile
index 660532a..9746c25 100644
--- a/Gemfile
+++ b/Gemfile
@@ -71,7 +71,7 @@ group :development do
 end
 
 group :production do
-  gem 'mysql2'
+  gem 'mysql2', '~> 0.3.0'
 end
 
 gem 'high_voltage', '~> 2.4.0'
diff --git a/Gemfile.lock b/Gemfile.lock
index f24eedc..b4cde59 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -246,7 +246,7 @@ DEPENDENCIES
   jbuilder (~> 2.0)
   jquery-datatables-rails (~> 3.3.0)
   jquery-rails
-  mysql2
+  mysql2 (~> 0.3.0)
   omniauth-oauth2
   purecss-rails
   rails (= 4.2.4)
diff --git a/db/migrate/20150908091546_create_transactions.rb b/db/migrate/20150908091546_create_transactions.rb
index de40fa3..dda51f7 100644
--- a/db/migrate/20150908091546_create_transactions.rb
+++ b/db/migrate/20150908091546_create_transactions.rb
@@ -1,13 +1,16 @@
 class CreateTransactions < ActiveRecord::Migration
   def change
     create_table :transactions do |t|
-      t.references :debtor, index: true, foreign_key: true, null: false
-      t.references :creditor, index: true, foreign_key: true, null: false
+      t.references :debtor, index: true, null: false
+      t.references :creditor, index: true, null: false
       t.integer :amount, null: false, default: 0
       t.string :origin, null: false
       t.string :message
 
       t.timestamps null: false
     end
+
+    add_foreign_key :transactions, :users, column: :creditor_id
+    add_foreign_key :transactions, :users, column: :debtor_id
   end
 end