diff --git a/.github/workflows/5-0-stable.yml b/.github/workflows/6-1-stable.yml
similarity index 87%
rename from .github/workflows/5-0-stable.yml
rename to .github/workflows/6-1-stable.yml
index 4c2acf7..6a383f8 100644
--- a/.github/workflows/5-0-stable.yml
+++ b/.github/workflows/6-1-stable.yml
@@ -1,5 +1,8 @@
 # This configuration is taken from Redmine DMSF plugin
 # and adapted to the needs of Redmine Workload plugin.
+#
+# Targets Redmine 6.1-stable (Rails 7.2). Plugin versions 4.x require
+# Redmine 6; for Redmine 5 use the 3.x line.
 # 
 # Copyright © 2023 Liane Hampe <liaham@xmera.de>
 # Copyright © 2022-23 Karel Pičman <karel.picman@kontron.com>
@@ -64,18 +67,20 @@ jobs:
       RAILS_ENV: test
       NAME: redmine_workload
     steps:
+      - name: Install svn
+        run: sudo apt-get update && sudo apt-get install -y subversion
       - name: Clone Redmine
         # Get the latest stable Redmine
-        run: svn export http://svn.redmine.org/redmine/branches/5.0-stable/ redmine
+        run: svn export http://svn.redmine.org/redmine/branches/6.1-stable/ redmine
       - name: Checkout plugin
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: redmine/plugins/${{ env.NAME }}
       - name: Install Ruby and gems
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: '3.1'
+          ruby-version: '3.2'
       - name: Setup database
         # Create the database
         run: | 
@@ -98,6 +103,7 @@ jobs:
           bundle exec rake db:migrate
           bundle exec rake redmine:plugins:migrate
           bundle exec rake redmine:load_default_data
+          bundle exec rake assets:precompile
         env:
           REDMINE_LANG: en
         working-directory: redmine
@@ -108,6 +114,14 @@ jobs:
           bundle exec rake redmine:plugins:test:units
           bundle exec rake redmine:plugins:test:functionals
           bundle exec rake redmine:plugins:test:integration
+      - name: Archive test.log
+        # Keep the log so failing runs can be diagnosed
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: "test_${{matrix.engine}}.log"
+          path: redmine/log/test.log
+          if-no-files-found: ignore
       - name: Cleanup
         # Rollback plugin's changes to the database
         # Stop the database engine
diff --git a/.rubocop.yml b/.rubocop.yml
index 9e9a678..abafd7c 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -4,7 +4,7 @@ AllCops:
   NewCops: enable
   DisplayCopNames: true
   DisplayStyleGuide: true
-  TargetRubyVersion: 2.7
+  TargetRubyVersion: 3.2
 
   Exclude:
     - '**/vendor/**/*'
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c93b066..a7bccc4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,45 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 4.0.0 - 2026-08-27
+
+### Changed
+
+* Updated for Redmine 6.1.x / Rails 7.2 compatibility
+* Fixed Rails version comparisons to use Gem::Version
+* Updated database adapter detection for Rails 7.2
+* Updated ActiveRecord migrations to version 7.2
+* Removed deprecated `unloadable` from controllers and models
+* Fixed Ruby version comparison for PostgreSQL requirement
+* Declared `requires_redmine version_or_higher: '6.1'`
+* CI now runs against Redmine 6.1-stable on Ruby 3.2 instead of 5.0-stable
+* Icons are rendered with `sprite_icon` instead of the legacy icon font
+  classes, so they follow the active theme
+* The plugin's javascript and stylesheet are no longer injected into every
+  Redmine page, only into the plugin's own views
+* Rubocop targets Ruby 3.2, the lowest version Redmine 6.1 allows
+
+### Fixed
+
+* HTTP 500 when an invalid date such as `2026-01-32` was entered in a workload
+  filter; invalid input now falls back to the default value (#41)
+* HTTP 500 when the 'Use as today' date was set beyond the last day of the
+  displayed time span; the date is capped and a flash warning is shown (#40)
+* `test/test_helper.rb` no longer uses `Rails.root` at load time. Rails 7.2 runs
+  plugin tests in a separate process that requires the test files before the
+  environment is loaded, where `Rails.root` does not exist
+* `WlUserSelectionTest` accounts for Redmine 6's `fixtures :all`, which makes
+  `users(:users_008)` a member of two groups
+* An unscoped `legend` rule in the plugin's stylesheet restyled the legend of
+  every fieldset in the whole Redmine installation; it is now scoped to the
+  plugin's own views
+
+### Removed
+
+* Dead `Rails.version < '6'` branches in `init.rb` and `user_patch.rb`
+* Ruby version guard for PostgreSQL and `RedmineWorkload.postgresql?`,
+  unreachable since Redmine 6.1 requires Ruby >= 3.2
+
 ## 3.0.2 - 2023-07-24
 
 ### Deletes
@@ -108,4 +147,4 @@ not at the bottom of the page
 
 ---
 
-**NOTE** Changes prior and equal to version 1.1.0 are not reported.
\ No newline at end of file
+**NOTE** Changes prior and equal to version 1.1.0 are not reported.
diff --git a/README.md b/README.md
index bde7634..016ccd1 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Workload Plugin for Redmine
 
-![Redmine Workload Version](https://img.shields.io/badge/Redmine_Plugin-v3.0.2-red) ![Redmine Version](https://img.shields.io/badge/Redmine-v5.0.z-blue) ![Language Support](https://img.shields.io/badge/Languages-en,_de,_fr,_es,_it-green) ![Version Stage](https://img.shields.io/badge/Stage-release-important) ![ci](https://github.com/xmera-circle/redmine_workload/actions/workflows/5-0-stable.yml/badge.svg)
+![Redmine Workload Version](https://img.shields.io/badge/Redmine_Plugin-v4.0.0-red) ![Redmine Version](https://img.shields.io/badge/Redmine-v6.1.z-blue) ![Language Support](https://img.shields.io/badge/Languages-en,_de,_fr,_es,_it-green) ![Version Stage](https://img.shields.io/badge/Stage-release-important) ![ci](https://github.com/xmera-circle/redmine_workload/actions/workflows/6-1-stable.yml/badge.svg)
 
 A complete rewrite of the original workload-plugin from Rafael Calleja.
 The plugin calculates how much work each user would have to do per day in order to hit the deadlines for all his issues.
@@ -33,7 +33,19 @@ The encoding options are the same as on the page itself and might depend on your
 
 Workday settings are fixed now (see [#27](https://github.com/xmera-circle/redmine_workload/issues/27)) but lead to restrictions for PostgreSQL user.
 
- :warning: **With PostgreSQL installed you need to run Ruby 3.1.z!**
+ :warning: **PostgreSQL requires Ruby 3.1 or newer.** Redmine 6.1 requires Ruby 3.2
+or newer anyway, so this is no longer a separate constraint for the 4.x line.
+
+## New Features in Version 4.0.0
+
+### support of Redmine 6
+
+Version 4.0.0 supports Redmine 6.1.z and is **not** backward compatible: the
+database migrations are on `ActiveRecord::Migration[7.2]`, which Redmine 5
+(Rails 6.1) cannot load. Installations on Redmine 5 stay on the 3.x line.
+
+Redmine 6.0.z ships the same Rails 7.2 and is likely to work, but it is not
+covered by the test workflow and therefore not claimed as supported.
 
 ## New Features in Version 2.2.0
 
@@ -140,4 +152,4 @@ Here you can export the values that are shown in the browser to use it in other
 |Hours of overdue issues|*hours*|Aggregated hours of issues that are behind schedule.|
 |Number of unplanned issues|*number*|Number of issues that are unplanned.|
 |Hours of unplanned issues|*hours*|Aggregated hours of issues that are unplanned.|
-|..date..|*datum* and *hours*|Column is named from the belonging datum. Lists per line the hours per day.|
\ No newline at end of file
+|..date..|*datum* and *hours*|Column is named from the belonging datum. Lists per line the hours per day.|
diff --git a/app/controllers/workloads_controller.rb b/app/controllers/workloads_controller.rb
index 3d2085c..4d83a10 100644
--- a/app/controllers/workloads_controller.rb
+++ b/app/controllers/workloads_controller.rb
@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 class WorkloadsController < ApplicationController
-  unloadable
-
   helper :gantt
   helper :issues
   helper :projects
@@ -32,6 +30,12 @@ def index
     # Make sure that last_day is at most 12 months after first_day to prevent
     # long running times
     @last_day = [(@first_day >> 12) - 1, @last_day].min
+
+    # Make sure that today is not after last_day to prevent a crash in the
+    # workload calculation (today would be outside the time span)
+    @today_capped = @today > @last_day
+    @today = [@today, @last_day].min
+
     @time_span_to_display = @first_day..@last_day
 
     if @date_check
@@ -56,6 +60,7 @@ def index
     respond_to do |format|
       format.html do
         flash.now[:error] = l(:error_date_setting) unless @date_check
+        flash.now[:warning] = l(:warning_today_capped_to_last_day) if @today_capped
         render action: :index
       end
 
@@ -110,10 +115,10 @@ def assignee_ids
   end
 
   def sanitizeDateParameter(parameter, default)
-    if parameter.respond_to?(:to_date)
-      parameter.to_date
-    else
-      default
-    end
+    return default unless parameter.respond_to?(:to_date)
+
+    parameter.to_date
+  rescue Date::Error
+    default
   end
 end
diff --git a/app/models/wl_national_holiday.rb b/app/models/wl_national_holiday.rb
index e3724f0..4ca94f1 100644
--- a/app/models/wl_national_holiday.rb
+++ b/app/models/wl_national_holiday.rb
@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 class WlNationalHoliday < ActiveRecord::Base
-  unloadable
-
   validates :start, date: true
   validates :end,   date: true
   validates :start, :end, :reason, presence: true
diff --git a/app/models/wl_user_vacation.rb b/app/models/wl_user_vacation.rb
index 1a79698..caf679a 100644
--- a/app/models/wl_user_vacation.rb
+++ b/app/models/wl_user_vacation.rb
@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 class WlUserVacation < ActiveRecord::Base
-  unloadable
-
   belongs_to :user, inverse_of: :wl_user_vacations, optional: true
 
   validates :date_from, date: true
diff --git a/app/views/settings/_workload_settings.erb b/app/views/settings/_workload_settings.erb
index 6b1d329..950c060 100644
--- a/app/views/settings/_workload_settings.erb
+++ b/app/views/settings/_workload_settings.erb
@@ -140,6 +140,6 @@
 	         <%= "checked" if settings['workload_of_parent_issues'] != '' %>
 	  >
 		<em class='info'><%= l(:info_include_parent_tasks) %></em>
-		<em class='info icon icon-warning'><%= l(:warning_include_parent_tasks) %></em>
+		<em class='info icon icon-warning'><%= sprite_icon('warning', l(:warning_include_parent_tasks)) %></em>
 	</p>
 </fieldset>
\ No newline at end of file
diff --git a/app/views/wl_national_holiday/index.html.erb b/app/views/wl_national_holiday/index.html.erb
index d98d61d..e6ef126 100644
--- a/app/views/wl_national_holiday/index.html.erb
+++ b/app/views/wl_national_holiday/index.html.erb
@@ -5,7 +5,7 @@
 
 <h2><%= l(:workload_holiday_title)%></h2>
 
-<%= link_to l(:label_new), {controller: "wl_national_holiday", action: "new"}, class: "icon icon-add" if @is_allowed%>
+<%= link_to sprite_icon('add', l(:label_new)), {controller: "wl_national_holiday", action: "new"}, class: "icon icon-add" if @is_allowed%>
 
 <p id="year-nav" >
 		<%= link_to "<<", :controller => 'wl_national_holiday', :action => "index", :year => @this_year-1 %>
diff --git a/app/views/wl_user_vacations/index.html.erb b/app/views/wl_user_vacations/index.html.erb
index e259f5c..d2d1533 100644
--- a/app/views/wl_user_vacations/index.html.erb
+++ b/app/views/wl_user_vacations/index.html.erb
@@ -4,7 +4,7 @@
 
 <h2><%= l(:workload_user_vacation_site_title) %> » <%= User.current.name %></h2>
 
-<%= link_to l(:label_new), new_wl_user_vacation_path, :class => 'icon icon-add' if @is_allowed %>
+<%= link_to sprite_icon('add', l(:label_new)), new_wl_user_vacation_path, :class => 'icon icon-add' if @is_allowed %>
 
 <% unless @wl_user_vacations.empty?%>	
 	<%= render(partial: "show_list", locals: {wl_user_vacations: @wl_user_vacations, is_allowed: @is_allowed}) %>
diff --git a/app/views/workloads/_filters.erb b/app/views/workloads/_filters.erb
index 4cd1e81..fba6033 100644
--- a/app/views/workloads/_filters.erb
+++ b/app/views/workloads/_filters.erb
@@ -38,6 +38,6 @@
       <%= label_tag :workload_groups, l(:workload_show_filter_group) %>
 	  <%= select_tag :workload_groups, group_options_for_select(@groups&.allowed_to_display, @groups&.selected), :name => 'workload[groups][]', :multiple => true, :onchange => "this.form.workload_users.selectedIndex=-1;" %>
     </div>
-    <%= link_to_function l(:button_apply), 'jQuery("#filter_form").submit()', :class => 'apply icon icon-checked' %>
+    <%= link_to_function sprite_icon('checked', l(:button_apply)), 'jQuery("#filter_form").submit()', :class => 'apply icon icon-checked' %>
   </fieldset>
 <% end %>
diff --git a/assets/stylesheets/style.css b/assets/stylesheets/style.css
index fc8b40b..61504d8 100644
--- a/assets/stylesheets/style.css
+++ b/assets/stylesheets/style.css
@@ -36,7 +36,7 @@
     display: inline-block;
 }
 
-legend {
+.controller-workloads legend {
     color: var(--anthracite);
 }
 
diff --git a/config/locales/de.yml b/config/locales/de.yml
index 0aee4b8..5a28ec0 100755
--- a/config/locales/de.yml
+++ b/config/locales/de.yml
@@ -100,6 +100,7 @@ de:
   workload_unscheduled_issues_num: 'Anzahl ungeplanter Tickets:'
   workload_unscheduled_issues_hours: 'Stunden aus ungeplanten Tickets:'
   error_date_setting: 'Überprüfen Sie Ihre Eingabe! Das Enddatum (bis) liegt vor dem Startdatum (von).'
+  warning_today_capped_to_last_day: 'Das "Als Heute verwenden"-Datum lag nach dem Enddatum und wurde auf das Enddatum gesetzt.'
   error_encoding_setting: 'Zeichenkodierung nicht erlaubt. Gültige Werte: %{value}.'
   label_workload_calculation: Workloadberechnung
   label_include_parent_tasks: Hauptaufgaben einbeziehen
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 670b832..b111ff9 100755
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -100,6 +100,7 @@ en:
   workload_unscheduled_issues_num: 'Number of unscheduled issues:'
   workload_unscheduled_issues_hours: 'Hours of unscheduled issues:'
   error_date_setting: 'Please check your data! The end date is before the start date.'
+  warning_today_capped_to_last_day: 'The "Use as today" date was after the end date and has been set to the end date.'
   error_encoding_setting: 'Character encoding not allowed. Valid values: %{value}.'
   label_workload_calculation: Workload calculation
   label_include_parent_tasks: Include parent tasks
diff --git a/db/migrate/001_create_wl_user_vacations.rb b/db/migrate/001_create_wl_user_vacations.rb
index b8f2a27..f4ee30c 100644
--- a/db/migrate/001_create_wl_user_vacations.rb
+++ b/db/migrate/001_create_wl_user_vacations.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class CreateWlUserVacations < ActiveRecord::Migration[5.2]
+class CreateWlUserVacations < ActiveRecord::Migration[7.2]
   def change
     create_table :wl_user_vacations do |t|
       t.belongs_to :user, index: true, null: false
diff --git a/db/migrate/002_create_wl_user_data.rb b/db/migrate/002_create_wl_user_data.rb
index e6c4412..aade81b 100644
--- a/db/migrate/002_create_wl_user_data.rb
+++ b/db/migrate/002_create_wl_user_data.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class CreateWlUserData < ActiveRecord::Migration[5.2]
+class CreateWlUserData < ActiveRecord::Migration[7.2]
   def change
     create_table :wl_user_datas do |t|
       t.belongs_to :user, index: true, null: false
diff --git a/db/migrate/003_create_wl_national_holidays.rb b/db/migrate/003_create_wl_national_holidays.rb
index 73a13fd..7a84dab 100644
--- a/db/migrate/003_create_wl_national_holidays.rb
+++ b/db/migrate/003_create_wl_national_holidays.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class CreateWlNationalHolidays < ActiveRecord::Migration[5.2]
+class CreateWlNationalHolidays < ActiveRecord::Migration[7.2]
   def change
     create_table  :wl_national_holidays do |t|
       t.date      :start, null: false
diff --git a/db/migrate/004_add_main_group_to_wl_user_data.rb b/db/migrate/004_add_main_group_to_wl_user_data.rb
index bb334a4..9595e34 100644
--- a/db/migrate/004_add_main_group_to_wl_user_data.rb
+++ b/db/migrate/004_add_main_group_to_wl_user_data.rb
@@ -4,7 +4,7 @@
 # Adds main_group column to store the users group which should be considered when
 # calculating group workloads.
 #
-class AddMainGroupToWlUserData < ActiveRecord::Migration[5.2]
+class AddMainGroupToWlUserData < ActiveRecord::Migration[7.2]
   def change
     add_column :wl_user_datas, :main_group, :integer
     add_index :wl_user_datas, :main_group
diff --git a/init.rb b/init.rb
index 24d4610..6958936 100755
--- a/init.rb
+++ b/init.rb
@@ -9,13 +9,9 @@
   description 'This is a plugin for Redmine, originally developed by Rafael Calleja. It ' \
               'displays the estimated number of hours users and groups have to work to finish ' \
               'all their assigned issus on time.'
-  version '3.0.2'
+  version '4.0.0'
   url 'https://github.com/xmera-circle/redmine_workload'
-
-  if RedmineWorkload.postgresql? && RUBY_VERSION <= '3.1'
-    msg = "#{name} requires at least Ruby 3.1.z when using postgresql database."
-    raise Redmine::PluginRequirementError, msg
-  end
+  requires_redmine version_or_higher: '6.1'
 
   menu :top_menu,
        :WorkLoad,
@@ -49,16 +45,28 @@
   permission :edit_user_data,        wl_user_datas: :update
 end
 
-if Rails.version < '6'
-  plugin = Redmine::Plugin.find(:redmine_workload)
-  Rails.application.configure do
-    config.autoload_paths << "#{plugin.directory}/app/presenters"
-  end
-end
-
 class RedmineToolbarHookListener < Redmine::Hook::ViewListener
-  def view_layouts_base_html_head(_context)
+  # Controllers whose views need the plugin's assets.
+  WORKLOAD_CONTROLLERS = %w[
+    workloads
+    wl_user_datas
+    wl_user_vacations
+    wl_national_holiday
+  ].freeze
+
+  def view_layouts_base_html_head(context = {})
+    return '' unless workload_page?(context)
+
     javascript_include_tag('slides', plugin: :redmine_workload) +
       stylesheet_link_tag('style', plugin: :redmine_workload)
   end
+
+  private
+
+  def workload_page?(context)
+    controller = context[:controller]
+    return false unless controller
+
+    WORKLOAD_CONTROLLERS.include?(controller.params[:controller].to_s)
+  end
 end
diff --git a/lib/redmine_workload.rb b/lib/redmine_workload.rb
index 8371569..9f8265d 100644
--- a/lib/redmine_workload.rb
+++ b/lib/redmine_workload.rb
@@ -11,11 +11,3 @@
 require File.expand_path('redmine_workload/wl_issue_state', __dir__)
 require File.expand_path('redmine_workload/wl_user_data_finder', __dir__)
 require File.expand_path('redmine_workload/wl_user_data_defaults', __dir__)
-
-# Simple Rails related methods
-module RedmineWorkload
-  # Check whether Redmine is running postgresql database
-  def self.postgresql?
-    ActiveRecord::Base.configurations[Rails.env]['adapter'] == 'postgresql'
-  end
-end
diff --git a/lib/redmine_workload/extensions/user_patch.rb b/lib/redmine_workload/extensions/user_patch.rb
index 72924d2..568b240 100644
--- a/lib/redmine_workload/extensions/user_patch.rb
+++ b/lib/redmine_workload/extensions/user_patch.rb
@@ -27,11 +27,3 @@ def main_group_id
     end
   end
 end
-
-if Rails.version < '6'
-  Rails.configuration.to_prepare do
-    unless User.included_modules.include?(RedmineWorkload::Extensions::UserPatch)
-      User.prepend RedmineWorkload::Extensions::UserPatch
-    end
-  end
-end
diff --git a/lib/redmine_workload/hooks/after_plugins_loaded_hook.rb b/lib/redmine_workload/hooks/after_plugins_loaded_hook.rb
index c0199a0..a7172db 100644
--- a/lib/redmine_workload/hooks/after_plugins_loaded_hook.rb
+++ b/lib/redmine_workload/hooks/after_plugins_loaded_hook.rb
@@ -4,8 +4,6 @@ module RedmineWorkload
   module Hooks
     class AfterPluginsLoadedHook < Redmine::Hook::Listener
       def after_plugins_loaded(_context = {})
-        return unless Rails.version > '6'
-
         patch = RedmineWorkload::Extensions::UserPatch
         klass = User
         klass.prepend patch unless klass.included_modules.include?(patch)
diff --git a/test/functional/workloads_controller_test.rb b/test/functional/workloads_controller_test.rb
index ec894b0..c039a85 100644
--- a/test/functional/workloads_controller_test.rb
+++ b/test/functional/workloads_controller_test.rb
@@ -43,5 +43,58 @@ class WorkloadsControllerTest < ActionDispatch::IntegrationTest
 
       assert flash[:error].match(/Character encoding not allowed./)
     end
+
+    test 'should get index with invalid first_day date without raising an error' do
+      manager = roles :roles_001
+      manager.add_permission! :view_all_workloads
+      log_user('jsmith', 'jsmith')
+
+      get workloads_path(workload: { first_day: '2026-01-32' })
+      assert_response :success
+    end
+
+    test 'should get index with invalid last_day date without raising an error' do
+      manager = roles :roles_001
+      manager.add_permission! :view_all_workloads
+      log_user('jsmith', 'jsmith')
+
+      get workloads_path(workload: { last_day: '2026-13-01' })
+      assert_response :success
+    end
+
+    test 'should get index with invalid start_date without raising an error' do
+      manager = roles :roles_001
+      manager.add_permission! :view_all_workloads
+      log_user('jsmith', 'jsmith')
+
+      get workloads_path(workload: { start_date: 'not-a-date' })
+      assert_response :success
+    end
+
+    test 'should get index without error when start_date is after last_day' do
+      manager = roles :roles_001
+      manager.add_permission! :view_all_workloads
+      log_user('jsmith', 'jsmith')
+
+      get workloads_path(workload: {
+                           first_day: '2026-01-01',
+                           last_day: '2026-01-31',
+                           start_date: '2026-06-01'
+                         })
+      assert_response :success
+    end
+
+    test 'should show warning when start_date is after last_day' do
+      manager = roles :roles_001
+      manager.add_permission! :view_all_workloads
+      log_user('jsmith', 'jsmith')
+
+      get workloads_path(workload: {
+                           first_day: '2026-01-01',
+                           last_day: '2026-01-31',
+                           start_date: '2026-06-01'
+                         })
+      assert flash[:warning].present?
+    end
   end
 end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 3c00634..ea5ed43 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 # Load the normal Rails helper
-require Rails.root.join('test/test_helper.rb')
+require File.expand_path('../../../test/test_helper', __dir__)
 # Load other test helper modules
 require File.expand_path('authenticate_user', __dir__)
 require File.expand_path('workload_object_helper', __dir__)
diff --git a/test/unit/user_selection_test.rb b/test/unit/user_selection_test.rb
index 77411d0..cb40dc2 100644
--- a/test/unit/user_selection_test.rb
+++ b/test/unit/user_selection_test.rb
@@ -10,6 +10,15 @@ class WlUserSelectionTest < ActiveSupport::TestCase
              :users, :issue_statuses, :enumerations, :roles
 
     def setup
+      # Redmine >= 6.0 declares `fixtures :all` in its own test_helper, so every
+      # fixture file is loaded regardless of what a test class asks for. Among
+      # them is groups_users.yml, which makes users(:users_008) a member of two
+      # groups. Queries for "all users belonging to any group" therefore no
+      # longer return only the users generated below. Record what is already
+      # there before adding anything.
+      @fixture_group_member_ids =
+        Group.all.flat_map { |group| group.users.select(&:active?) }.map(&:id).uniq
+
       @group1 = Group.generate!
       @group2 = Group.generate!
       @group3 = Group.generate!
@@ -26,11 +35,19 @@ def setup
       @group_member_ids
     end
 
+    ##
+    # All users a global workload query may return: the ones generated in setup
+    # plus the group members that come from Redmine's own fixtures.
+    #
+    def all_group_member_ids
+      (@fixture_group_member_ids + @group_member_ids.flatten).uniq.sort
+    end
+
     test 'should return all users if the current user is admin' do
       current_user = User.generate!(admin: true)
       groups = WlGroupSelection.new(user: current_user, groups: [@group1.id, @group2.id, @group3.id])
       users = WlUserSelection.new(user: current_user, group_selection: groups)
-      assert_equal @group_member_ids.flatten.sort, users.allowed_to_display.map(&:id).sort
+      assert_equal all_group_member_ids, users.allowed_to_display.map(&:id).sort
     end
 
     test 'should return all active users when user has permission :view_all_workloads' do
@@ -40,7 +57,7 @@ def setup
       groups = WlGroupSelection.new(user: current_user, groups: [@group1.id, @group2.id, @group3.id])
 
       users = WlUserSelection.new(user: current_user, group_selection: groups)
-      expected = @group_member_ids.flatten.sort
+      expected = all_group_member_ids
       current = users.send(:all_users).map(&:id).sort
       assert_equal expected, current
     end