diff --git a/app/models/issue.rb b/app/models/issue.rb
index 97c97e910..7807d2859 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -64,7 +64,6 @@ class Issue < ActiveRecord::Base
         lambda {|*args| { :include => :project,
                           :conditions => Issue.visible_condition(args.shift || User.current, *args) } }
 
-  class << self; undef :open; end
   scope :open, lambda {|*args|
     is_closed = args.size > 0 ? !args.first : false
     {:conditions => ["#{IssueStatus.table_name}.is_closed = ?", is_closed], :include => :status}
diff --git a/app/models/version.rb b/app/models/version.rb
index 49b91b87f..cd32da91e 100644
--- a/app/models/version.rb
+++ b/app/models/version.rb
@@ -35,7 +35,6 @@ class Version < ActiveRecord::Base
   validates_inclusion_of :sharing, :in => VERSION_SHARINGS
 
   scope :named, lambda {|arg| { :conditions => ["LOWER(#{table_name}.name) = LOWER(?)", arg.to_s.strip]}}
-  class << self; undef :open; end
   scope :open, :conditions => {:status => 'open'}
   scope :visible, lambda {|*args| { :include => :project,
                                           :conditions => Project.allowed_to_condition(args.first || User.current, :view_issues) } }
diff --git a/config/initializers/10-patches.rb b/config/initializers/10-patches.rb
index 672f1c0a0..e4a110cfa 100644
--- a/config/initializers/10-patches.rb
+++ b/config/initializers/10-patches.rb
@@ -10,6 +10,11 @@ module ActiveRecord
       l("field_#{name.underscore.gsub('/', '_')}_#{attr}", :default => ["field_#{attr}".to_sym, attr])
     end
   end
+
+  # Undefines private Kernel#open method to allow using `open` scopes in models.
+  # See Defect #11545 (http://www.redmine.org/issues/11545) for details.
+  class Base ; undef open ; end
+  class Relation ; undef open ; end
 end
 
 module ActionView
diff --git a/test/unit/project_test.rb b/test/unit/project_test.rb
index 64a2631ea..3abfbe327 100644
--- a/test/unit/project_test.rb
+++ b/test/unit/project_test.rb
@@ -132,6 +132,10 @@ class ProjectTest < ActiveSupport::TestCase
     end
   end
 
+  def test_open_scope_on_issues_association
+    assert_kind_of Issue, Project.find(1).issues.open.first
+  end
+
   def test_archive
     user = @ecookbook.members.first.user
     @ecookbook.archive