diff --git a/backend/app/models/nico_tag_relation.rb b/backend/app/models/nico_tag_relation.rb
index ff4f3a6..d2c4a82 100644
--- a/backend/app/models/nico_tag_relation.rb
+++ b/backend/app/models/nico_tag_relation.rb
@@ -6,6 +6,7 @@ class NicoTagRelation < ApplicationRecord
   validates :tag_id, presence: true
 
   validate :nico_tag_must_be_nico
+  validate :tag_mustnt_be_nico
 
   private