diff --git a/app/models/epp_session.rb b/app/models/epp_session.rb
index dd97a91a9..3d489e567 100644
--- a/app/models/epp_session.rb
+++ b/app/models/epp_session.rb
@@ -2,5 +2,5 @@ class EppSession < ActiveRecord::Base
   belongs_to :user, required: true
   belongs_to :registrar
 
-  validates :session_id, presence: true
+  validates :session_id, uniqueness: true, presence: true
 end
diff --git a/test/models/epp_session_test.rb b/test/models/epp_session_test.rb
index a6aca3eca..497bf441e 100644
--- a/test/models/epp_session_test.rb
+++ b/test/models/epp_session_test.rb
@@ -20,4 +20,18 @@ class EppSessionTest < ActiveSupport::TestCase
     @epp_session.validate
     assert @epp_session.invalid?
   end
+
+  def test_invalid_if_persisted_record_with_the_same_session_id_exists
+    epp_session = EppSession.new(session_id: @epp_session.session_id, user: @epp_session.user)
+    epp_session.validate
+    assert epp_session.invalid?
+  end
+
+  def test_database_session_id_unique_constraint
+    epp_session = EppSession.new(session_id: @epp_session.session_id, user: @epp_session.user)
+
+    assert_raises ActiveRecord::RecordNotUnique do
+      epp_session.save(validate: false)
+    end
+  end
 end