diff --git a/db/migrate/20140304005354_add_index_merge_request_diffs_on_merge_request_id.rb b/db/migrate/20140304005354_add_index_merge_request_diffs_on_merge_request_id.rb
new file mode 100644
index 0000000000000000000000000000000000000000..65d28e8cb01f1afeb4bed9ffe660bf48e90f6f48
--- /dev/null
+++ b/db/migrate/20140304005354_add_index_merge_request_diffs_on_merge_request_id.rb
@@ -0,0 +1,5 @@
+class AddIndexMergeRequestDiffsOnMergeRequestId < ActiveRecord::Migration
+  def change
+    add_index :merge_request_diffs, :merge_request_id, unique: true
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 4f6d942eeb320a48c793f242043b3590018005fe..9f1de4d21203f2686f554ede6cfe14ee7cf2e72d 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: 20140214102325) do
+ActiveRecord::Schema.define(version: 20140304005354) do
 
   create_table "broadcast_messages", force: true do |t|
     t.text     "message",    null: false
@@ -114,6 +114,8 @@ ActiveRecord::Schema.define(version: 20140214102325) do
     t.datetime "updated_at"
   end
 
+  add_index "merge_request_diffs", ["merge_request_id"], name: "index_merge_request_diffs_on_merge_request_id", unique: true, using: :btree
+
   create_table "merge_requests", force: true do |t|
     t.string   "target_branch",     null: false
     t.string   "source_branch",     null: false