diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 6e3fe213b..b08bd8eb9 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -395,7 +395,6 @@ Lint/IneffectiveAccessModifier:
     - 'app/models/mail_handler.rb'
     - 'app/models/mailer.rb'
     - 'app/models/user.rb'
-    - 'lib/redmine/helpers/gantt.rb'
     - 'lib/redmine/scm/adapters/abstract_adapter.rb'
 
 Lint/InterpolationCheck:
diff --git a/lib/redmine/helpers/gantt.rb b/lib/redmine/helpers/gantt.rb
index 2258faf9c..db0676ba7 100644
--- a/lib/redmine/helpers/gantt.rb
+++ b/lib/redmine/helpers/gantt.rb
@@ -667,23 +667,26 @@ module Redmine
         start_date + (end_date - start_date + 1) * (progress / 100.0)
       end
 
-      def self.sort_issues!(issues)
-        issues.sort_by! {|issue| sort_issue_logic(issue)}
-      end
+      # Singleton class method is public
+      class << self
+        def sort_issues!(issues)
+          issues.sort_by! {|issue| sort_issue_logic(issue)}
+        end
 
-      def self.sort_issue_logic(issue)
-        julian_date = Date.new()
-        ancesters_start_date = []
-        current_issue = issue
-        begin
-          ancesters_start_date.unshift([current_issue.start_date || julian_date, current_issue.id])
-          current_issue = current_issue.parent
-        end while (current_issue)
-        ancesters_start_date
-      end
+        def sort_issue_logic(issue)
+          julian_date = Date.new()
+          ancesters_start_date = []
+          current_issue = issue
+          begin
+            ancesters_start_date.unshift([current_issue.start_date || julian_date, current_issue.id])
+            current_issue = current_issue.parent
+          end while (current_issue)
+          ancesters_start_date
+        end
 
-      def self.sort_versions!(versions)
-        versions.sort!
+        def sort_versions!(versions)
+          versions.sort!
+        end
       end
 
       def pdf_new_page?(options)