diff --git a/app/helpers/avatars_helper.rb b/app/helpers/avatars_helper.rb
index 6aa92b1cf..f8ddcc41e 100644
--- a/app/helpers/avatars_helper.rb
+++ b/app/helpers/avatars_helper.rb
@@ -62,10 +62,12 @@ module AvatarsHelper
   end
 
   def anonymous_avatar(options={})
+    options[:class] = ['anonymous-avatar', options[:class]].compact.join(' ')
     image_tag 'anonymous.png', GravatarHelper::DEFAULT_OPTIONS.except(:default, :rating, :ssl).merge(options)
   end
 
   def group_avatar(options={})
+    options[:class] = ['group-avatar', options[:class]].compact.join(' ')
     image_tag 'group.png', GravatarHelper::DEFAULT_OPTIONS.except(:default, :rating, :ssl).merge(options)
   end
 
diff --git a/test/helpers/avatars_helper_test.rb b/test/helpers/avatars_helper_test.rb
index dee529b69..1ceba909d 100644
--- a/test/helpers/avatars_helper_test.rb
+++ b/test/helpers/avatars_helper_test.rb
@@ -36,11 +36,17 @@ class AvatarsHelperTest < Redmine::HelperTest
   end
 
   def test_avatar_with_anonymous_user
-    assert_match %r{src="/assets/anonymous(-\w+)?.png"}, avatar(User.anonymous)
+    avatar_tag = avatar(User.anonymous)
+
+    assert_match %r{src="/assets/anonymous(-\w+)?.png"}, avatar_tag
+    assert_match 'class="anonymous-avatar avatar"', avatar_tag
   end
 
   def test_avatar_with_group
-    assert_match %r{src="/assets/group(-\w+)?.png"}, avatar(Group.first)
+    avatar_tag = avatar(Group.first)
+
+    assert_match %r{src="/assets/group(-\w+)?.png"}, avatar_tag
+    assert_match 'class="group-avatar avatar"', avatar_tag
   end
 
   def test_avatar_with_invalid_arg_should_return_nil