diff --git a/app/models/reviewable.rb b/app/models/reviewable.rb
index 280c7515f9a..dce29398645 100644
--- a/app/models/reviewable.rb
+++ b/app/models/reviewable.rb
@@ -36,6 +36,8 @@ class Reviewable < ActiveRecord::Base
   enum :priority, { low: 0, medium: 5, high: 10 }, scopes: false, suffix: true
   enum :sensitivity, { disabled: 0, low: 9, medium: 6, high: 3 }, scopes: false, suffix: true
 
+  validates :reject_reason, length: { maximum: 500 }
+
   after_create { log_history(:created, created_by) }
 
   after_commit(on: :create) { DiscourseEvent.trigger(:reviewable_created, self) }
diff --git a/spec/models/reviewable_spec.rb b/spec/models/reviewable_spec.rb
index 11893546c29..88711fa7916 100644
--- a/spec/models/reviewable_spec.rb
+++ b/spec/models/reviewable_spec.rb
@@ -1,6 +1,10 @@
 # frozen_string_literal: true
 
 RSpec.describe Reviewable, type: :model do
+  describe "Validations" do
+    it { is_expected.to validate_length_of(:reject_reason).is_at_most(500) }
+  end
+
   describe ".create" do
     fab!(:admin) { Fabricate(:admin) }
     fab!(:user) { Fabricate(:user) }