diff --git a/app/models/user.rb b/app/models/user.rb
index b5fd9d0..5c62268 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -26,6 +26,7 @@ class User < ActiveRecord::Base
 
   default_scope order('username ASC')
 
+  validates :username, :presence => true, uniqueness: true
   validates :first_name, :presence => true
   validates :last_name, :presence => true