diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 88ba2674e..fd4554f0b 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -417,9 +417,15 @@ class ApplicationController < ActionController::Base
     url = params[:back_url]
     if url.nil? && referer = request.env['HTTP_REFERER']
       url = CGI.unescape(referer.to_s)
+      # URLs that contains the utf8=[checkmark] parameter added by Rails are
+      # parsed as invalid by URI.parse so the redirect to the back URL would
+      # not be accepted (ApplicationController#validate_back_url would return
+      # false)
+      url.gsub!(/(\?|&)utf8=\u2713&?/, '\1')
     end
     url
   end
+  helper_method :back_url
 
   def redirect_back_or_default(default, options={})
     back_url = params[:back_url].to_s
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index b76ade5d8..6a7812e4a 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -1425,19 +1425,6 @@ module ApplicationHelper
     arg.to_json.to_s.gsub('/', '\/').html_safe
   end
 
-  def back_url
-    url = params[:back_url]
-    if url.nil? && referer = request.env['HTTP_REFERER']
-      url = CGI.unescape(referer.to_s)
-      # URLs that contains the utf8=[checkmark] parameter added by Rails are
-      # parsed as invalid by URI.parse so the redirect to the back URL would
-      # not be accepted (ApplicationController#validate_back_url would return
-      # false)
-      url.gsub!(/(\?|&)utf8=\u2713&?/, '\1')
-    end
-    url
-  end
-
   def back_url_hidden_field_tag
     url = back_url
     hidden_field_tag('back_url', url, :id => nil) unless url.blank?
diff --git a/test/functional/application_controller_test.rb b/test/functional/application_controller_test.rb
new file mode 100644
index 000000000..abaa4a23e
--- /dev/null
+++ b/test/functional/application_controller_test.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+# Redmine - project management software
+# Copyright (C) 2006-2020  Jean-Philippe Lang
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+require File.expand_path('../../test_helper', __FILE__)
+
+class ApplicationControllerTest < Redmine::ControllerTest
+  def test_back_url_should_remove_utf8_checkmark_from_referer
+    @request.set_header 'HTTP_REFERER', "/path?utf8=\u2713&foo=bar"
+    assert_equal "/path?foo=bar", @controller.back_url
+  end
+end
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 2717b8d24..32b2740e2 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -1860,11 +1860,6 @@ class ApplicationHelperTest < Redmine::HelperTest
     assert !result.html_safe?
   end
 
-  def test_back_url_should_remove_utf8_checkmark_from_referer
-    stubs(:request).returns(stub(:env => {'HTTP_REFERER' => "/path?utf8=\u2713&foo=bar"}))
-    assert_equal "/path?foo=bar", back_url
-  end
-
   def test_hours_formatting
     set_language_if_valid 'en'