diff --git a/app/models/group.rb b/app/models/group.rb
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -1,8 +1,8 @@
 class Group < ActiveRecord::Base
-  has_many :groups_problems, class_name: GroupProblem
+  has_many :groups_problems, class_name: 'GroupProblem'
   has_many :problems, :through => :groups_problems
 
-  has_many :groups_users, class_name: GroupUser
+  has_many :groups_users, class_name: 'GroupUser'
   has_many :users, :through => :groups_users
 
   #has_and_belongs_to_many :problems