diff --git a/app/models/problem.rb b/app/models/problem.rb
--- a/app/models/problem.rb
+++ b/app/models/problem.rb
@@ -7,6 +7,9 @@
   has_many :groups_problems, class_name: GroupProblem
   has_many :groups, :through => :groups_problems
 
+  has_many :problems_tags, class_name: ProblemTag
+  has_many :tags, through: :problems_tags
+
   has_many :test_pairs, :dependent => :delete_all
   has_many :testcases, :dependent => :destroy