diff --git a/app/models/issue.rb b/app/models/issue.rb
index 0e634bf8b..d6b021546 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -257,6 +257,7 @@ class Issue < ActiveRecord::Base
   def reload(*args)
     @workflow_rule_by_attribute = nil
     @assignable_versions = nil
+    @assignable_users = nil
     @relations = nil
     @spent_hours = nil
     @total_spent_hours = nil
@@ -979,12 +980,12 @@ class Issue < ActiveRecord::Base
   def assignable_users
     return [] if project.nil?
 
-    users = project.assignable_users(tracker).to_a
-    users << author if author && author.active?
-    if assigned_to_id_was.present? && assignee = Principal.find_by_id(assigned_to_id_was)
-      users << assignee
-    end
-    users.uniq.sort
+    user_ids = []
+    user_ids << author_id if author&.active?
+    user_ids << assigned_to_id_was if assigned_to_id_was.present?
+    project_users = project.assignable_users(tracker)
+    user_ids.concat project_users.reorder(nil).ids
+    @assignable_users = user_ids.empty? ? [] : Principal.where(:id => user_ids).sorted.to_a
   end
 
   # Versions that the issue can be assigned to
diff --git a/test/unit/issue_test.rb b/test/unit/issue_test.rb
index b056ffb18..2e1fc5ae8 100644
--- a/test/unit/issue_test.rb
+++ b/test/unit/issue_test.rb
@@ -2595,6 +2595,15 @@ class IssueTest < ActiveSupport::TestCase
     assert_kind_of User, Issue.find(1).assignable_users.first
   end
 
+  test "#assignable_users should be sorted" do
+    %w(a č u ř c í ý š З д ч и).each do |firstname|
+      Member.create!(:project_id => 1, :principal => User.generate!(:firstname => firstname), :role_ids => [1])
+    end
+    issue = Issue.new(:project => Project.find(1))
+    assignable_users = Issue.find(1).assignable_users
+    assert_equal User.where(:id => assignable_users).sorted.pluck(:firstname), assignable_users.map(&:firstname)
+  end
+
   test "#assignable_users should include the issue author" do
     non_project_member = User.generate!
     issue = Issue.generate!(:author => non_project_member)