diff --git a/app/models/administrator.rb b/app/models/administrator.rb
index c82c4f728..15715a328 100644
--- a/app/models/administrator.rb
+++ b/app/models/administrator.rb
@@ -2,5 +2,5 @@ class Administrator < ActiveRecord::Base
   belongs_to :user
   delegate :name, :email, to: :user
 
-  validates :user_id, presence: true
+  validates :user_id, presence: true, uniqueness: true
 end
diff --git a/app/models/moderator.rb b/app/models/moderator.rb
index 6cfe0c291..30d4f4394 100644
--- a/app/models/moderator.rb
+++ b/app/models/moderator.rb
@@ -2,5 +2,5 @@ class Moderator < ActiveRecord::Base
   belongs_to :user
   delegate :name, :email, to: :user
 
-  validates :user_id, presence: true
+  validates :user_id, presence: true, uniqueness: true
 end